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Chemistry Research Guide

What is the CAS Registry Number?
Why do I need it?

Chemical Abstracts Service (CAS) has a registry system for all completely identified chemical compounds or substances. There are over 128 million chemical substances & sequences currently registered and 12,000 new substances are added every day!! Each individual chemical substance is assigned a CAS Registry Number which may be thought of as that substance's "Social Security number."  (For more information, see What does a CAS Registry Number look like?)

The rules of chemical nomenclature frequently change and each chemical substance is liable to have several names: i.e. trade or brand name(s); generic or common name(s); trivial or semisystematic name(s); and systematic or IUPAC name(s). For example, Tylenol is a brand name for acetaminophen which is itself a trivial name. The systematic name for this analgesic compound is Acetamide, N-(4-hydroxyphenyl)-. Another systematic name for this same compound is 4'-Hydroxyacetanilide. There is justone CAS registry number which is 103-90-2. Even if other names are created for this compound, the registry number will remain unchanged. There is no structural significance to the registry number - it is simply an identifier.

The most efficient and complete way to search for chemical substances in the Chemical Abstracts Online database is to use the CAS registry number(s).  A registry number may be searched as if it were a word, i.e., s 103-90-2 will search for information on Tylenol.  See Using Native Commands to Search Chemical Abstracts Online for more information on searching techniques.

CAS registry numbers are found in several print and electronic sources. These sources should be consulted before you develop your search strategy for Chemical Abstracts Online. It is a good idea to verify registry numbers found in sources not published by CAS. This is because the registry number could represent some other form of the compound (e.g., stereoisomer, salt, or an incompletely defined form) than the one you want. To verify the registry number, select the Registry File by typing  file reg  into the search box in Chemical Abstracts Online.  Enter s ###-##-# into the search box (###-##-# is the registry number - fill in the digits for the compound of interest). Check the record retrieved and make certain it is the desired substance before you use it in searching Chemical Abstracts Online.

If the substance retrieved is not the one you want or you cannot find the CAS registry number in any of the sources listed below, you may then search the Registry File by substance name or molecular formula. A structure search may be attempted if all else fails but this type of search is expensive and can be complicated.

General sources containing CAS Registry Numbers

  • Chemical Abstracts Index Guide. Columbus, OH: Chemical Abstracts Service, 1967-96 (ref QD 1 A51) There is an Index Guide for each collective 5-year period of Chemical Abstracts. The Index Guide is published every 18 months and cumulated at the end of each collective period. This is the "authority" list for both the print and online versions of Chemical Abstracts.
  • CRC Handbook of Chemistry and Physics. Cleveland, OH: CRC Press, published annually (ref QD 65 H3) *Older editions are in circulating collection (QD 65 H3).
  • Gardner, William, Gardner's Chemical Synonyms and Trade Names, 11th ed. Brookfield, VT: Gower, 1999 (ref TP 9 G286 1999)
  • Hawley, Gessner Goodrich, et al, Hawley's Condensed Chemical Dictionary, 15th ed. NY: Van Nostrand Reinhold, 2007 (ref QD 5 C5 2007)
  • Howard, Philip H. & Neal, Michael, Dictionary of Chemical Names and Synonyms, Boca Raton, FL: Lewis Publishers, 1992 (ref TP 9 H65 1992)
  • Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed. NY: Wiley, 1978-84 (ref TP 9 E685 1978) 25 volumes plus supplement.
  • Kirk-Othmer Encyclopedia of Chemical Technology, 4th ed. NY: Wiley, 1991 (ref TP 9 E685 1991) 25 volumes plus supplements.

Chemical catalogs containing CAS Registry Numbers

  • Aldrich Chemical Company, Aldrich Chemistry : Handbook of Fine Chemicals, Milwaukee, WI: Sigma-Aldrich (ref TP 202 A38)
  • Sigma Chemical Company, Biochemicals, Reagents & Kits for Life Science Research, St. Louis, MO: Sigma Chemical Co. (ref TP 202 S54)

Inorganic and Organic Compounds containing CAS Registry Numbers


  • Dictionary of Inorganic Compounds, 1st ed. NY: Chapman and Hall, 1992 (ref QD 148 D53 1992) 5-volume set and 1st-2nd annual supplements.


  • CRC Handbook of Data on Organic Compounds, 2nd ed. Boca Raton, FL: CRC Press, 1989 (ref QD 257.7 H36 1989) 10 volume set.
  • Dictionary of Organic Compounds, 5th ed. NY: Chapman and Hall, 1982 (ref QD 246 D5 1982) 7 volume set and 1st-10th annual supplements (1982-1992).
  • Handbook of Physical Properties of Organic Chemicals,  Boca Raton, FL: CRC Press, 1997  (ref  QD 257.7 H374 1997)
  • Pedley, J.B. Thermochemical Data of Organic Compounds, 2nd ed. NY: Chapman and Hall, 1986 (ref QD 511.8 P43 1986)

Drugs and Biologically Important Compunds containing CAS Registry Numbers

  • Dictionary of Alkaloids, London: Chapman and Hall, 1989 (ref RS 431 A53 D53 1989) 2 volume set. According to the introduction, it "includes most naturally occurring, nitrogen-containing secondary metabolites of plant, microbial, or even animal origin."
  • Merck Index, Rahway, NJ: Merck & Co., published every 7-8 years  (ref RS 51 M4)  Library has latest three editions.

Pesticides containing CAS Registry Numbers

  • Briggs, Shirley A. Basic Guide to Pesticides: their characteristics and hazards, Washington, DC: Hemisphere, 1992 (ref SB 951 B75 1992)
  • Crop Protection Handbook, Willoughby, OH: Meister PubCo, published annually. HSU Library has 2005 edition. (ref S 633 A5)
  • Montgomery, John H. Agrochemicals Desk Reference, 2nd edition.  Boca Raton, FL: CRC Press, 1997 (ref TD 196 A34 M66 1997)
  • Pesticide Index: an index of chemical, common and trade names of pesticides and related crop- protection products, Nottingham, England: Royal Society of Chemistry, 1988 (ref SB 950.95 P47 1988)
  • Worthing, Charles R. The Pesticide Manual, 9th ed. Surrey, UK: British Crop Protection Council, 1991 (ref SB 951 P434 1991)

Content Attribution

Some of the content of this page was created in another format by Sharon Chadwick, HSU Librarian, retired 06/2013. 

Toxic or Hazardous Substances containing CAS Registry Numbers

  • Beim, Howard J.  Rapid Guide to Hazardous Air Pollutants.  NY: Van Nostrand Reinhold, 1998 (ref TD 883.1 B37 1998)
  • Book of Lists for Regulated Hazardous Substances, 10th ed. Rockville, MD: The Institutes, 2001 (ref TD 1032 B66 2001)
  • Bretherick, L., Bretherick's Handbook of Reactive Chemical Hazards, 6th ed. Oxford ; Boston : Butterworth-Heinemann, 1999 (ref T 55.3 H3 B73 1999)
  • Bretherick, L., Hazards in the Chemical Laboratory, 4th ed. London: Royal Society of Chemistry, 1986 (ref QD 51 H35 1986)
  • Calabrese, Edward J. & Kenyon, Elaina M., Air Toxics and Risk Assessment. Chelsea, MI: Lewis Publishers, 1991 (ref RA 576.5 C35 1990)
  • Forum for Scientific Excellence, Inc., Compendium of Hazardous Chemicals in Schools and Colleges. Philadelphia, PA: Lippincott, 1990 (ref T 55.3 H3 C646 1990)
  • Forum for Scientific Excellence, Inc., Cross-reference Index of Hazardous Chemicals, Synonyms, and CAS Registry Numbers. Philadelphia, PA: J.B. Lippincott, 1990 (ref T 55.3 H3 C76 1990)
  • Forum for Scientific Excellence, Inc., Index of Hazardous Contents of Commercial Products in Schools and Colleges. Philadelphia, PA: J.B.Lippincott, 1990 (ref T 55.3 H3 I53 1990) Excellent way to find chemical components of trade name products.
  • Keith, Lawrence H. & Walker, Mary M., Handbook of Air Toxics: sampling, analysis, and properties. Boca Raton, FL: Lewis Publishers, 1995 (ref TD 890 K4 1995)
  • Kokoszka, Leopold, C., Environmental Management Handbook: toxic chemical materials and wastes. NY: Marcel Dekker, 1989 (ref TD 1032 K65 1989)
  • Lefevre, Marc J. & Conibear, Shirley A., First Aid Manual for Chemical Accidents, 2nd Engl. lang. ed. NY: Van Nostrand Reinhold, 1989 (ref RC 963.3 L4313 1989)
  • Lewis, Richard J., Sr., Carcinogenically Active Chemicals: a reference guide. NY: Van Nostrand Reinhold, 1991 (ref RC 268.6 L48 1991)
  • Lewis, Richard J., Sr., Food Additives Handbook. NY: Van Nostrand Reinhold, 1989 (ref RA 1270 F6 L49 1989)
  • Lewis, Richard J., Sr., Hazardous Chemicals Desk Reference, 5th ed. NY: Wiley, 2002  (ref T 55.3 H3 L49 2002)
  • Lewis, Richard J., Sr., & Sax, N. Irving, Sax's Dangerous Properties of Industrial Materials, 10th ed. NY: Wiley, 2000 (ref T55.3 H3 L494 2000) 3-volume set
  • Mackay, Donald, et al, Illustrated Handbook of Physical-Chemical Properties and Environmental Fate for Organic Chemicals. Boca Raton, FL: Lewis Publishers, 1992-1997 (ref TD 196 O73 M32 1992) 5-volume set
  • Mahn, William J., Academic Laboratory Chemical Hazards Guidebook. NY: Van Nostrand Reinhold, 1991 (ref QD 51 M29 1991)
  • Montgomery, John H. & Welkom, Linda M., Groundwater Chemicals Desk Reference, 3rd ed. Chelsea, MI: Lewis Publishers, 2000 (ref TD 426 M66 2000)
  • National Institute for Occupational Safety and Health, NIOSH Pocket Guide to Chemical Hazards. Cincinnati, OH: NIOSH, 1997 (Docs HE 20.7108:C42/997)
  • Pohanish, Richard P., Wiley Guide to Chemical Incompatibilities, 2nd ed. Hoboken NJ: J. Wiley, 2003  (ref T 55.3 H3 P647 2003)
  • Pohanish, Richard P., Rapid Guide to Hazardous Chemicals in the Environment. NY: Van Nostrand Reinhold, 1997  (ref RA 1226 P64 1997)
  • Pohanish, Richard P.,  Sittig's Handbook of Toxic and Hazardous Chemicals and Carcinogens, 4th ed. Park Ridge, NJ: Noyes Publications, 2002 (ref RA 1215 .S58 2002) 2-volume set
  • Proctor, Nick H., Proctor and Hughes' Chemical Hazards of the Workplace, 4th ed., NY: Van Nostrand Reinhold, 1996 (ref RA 1229 P76 1996)
  • Sheftel, Victor O., Handbook of Toxic Properties of Monomers and Additives. Boca Raton, FL: Lewis Publishers, 1995  (ref RA 1242 P66 S54 1995)
  • Shepard, Thomas H., Catalog of Teratogenic Agents, 11th ed. Baltimore, MD: Johns Hopkins University Press, 2004 (ref QM 691 S53 2004)
  • Sittig, Marshall, World-Wide Limits for Toxic and Hazardous Chemicals in Air, Water and Soil. Park Ridge, NJ: Noyes Publications, 1994 (ref RA 1229.5 S58 1994)