Learn more about how the Cal Poly Humboldt Library can help
support your research and learning needs.

Stay updated at Campus Ready.

Skip to Main Content

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 144 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, 16h ed. Hoboken, New Jersey: John Wiley & Sons, Incorporated,  2016
  • 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, 5th ed. NY: Wiley, 2004-2007, 26 volumes plus supplements.

Chemical catalogs containing CAS Registry Numbers

Inorganic and Organic Compounds containing CAS Registry Numbers



Drugs and Biologically Important Compunds containing CAS Registry Numbers

  • 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

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)
  • 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)
  • 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
  • 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)

Content Attribution

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