CAS number

A unique registry number assigned to a chemical substance by the Chemical Abstracts Service — the most widely used identifier for matching a compound across suppliers and literature.

A CAS Registry Number is assigned by the Chemical Abstracts Service to a specific chemical substance when it enters the registry, and the number stays with that substance permanently. The format is up to ten digits in three hyphen-separated groups, with a check digit at the end. Because assignment is centralised and curated, a CAS number is the closest thing chemistry has to a universal catalogue key.

For research compounds the identifier's value is disambiguation. Trade names and abbreviations collide and drift; a CAS number does not. Matching a product's CAS number against the registry confirms which substance a listing actually refers to — including, for peptides, which salt form, since salts can carry their own registry numbers distinct from the free base.

Coverage has limits. Novel and niche research compounds may have no assigned number, or an unverifiable one circulating on vendor sites. The identifiers published on this site's research pages are checked against the registry before publication, and a number that cannot be verified is dropped rather than repeated — several compounds here list no CAS number for exactly that reason.

SourceCAS — the CAS Registry

For research purposes only. Not for human consumption, diagnosis, treatment, or prevention of any condition. Nothing on this page is medical advice.