CAS REGISTRY is the most authoritative collection of disclosed chemical substance information, containing more than 68 million organic and inorganic substances and 63 million sequences (view current numbers).

CAS REGISTRY covers substances identified from the scientific literature from 1957 to the present, with additional substances going back to the early 1900s.

What is a CAS Registry Number (CAS RN)?

Each CAS Registry Number (often referred to as a CAS Number):

• Is a unique numeric identifier
• Designates only one substance
• Has no chemical significance
• Is a link to a wealth of information about a specific chemical substance

A CAS Registry Number is a numeric identifier that can contain up to 10 digits, divided by hyphens into three parts.

The right-most digit is a check digit used to verify the validity and uniqueness of the entire number.

For example, 58-08-2 is the CAS Registry Number for caffeine.

A CAS Registry Number is assigned to a substance when it enters the CAS REGISTRY database. Numbers are assigned in sequential order to unique, new substances identified by CAS scientists for inclusion in the database.

CAS REGISTRY contains a wide variety of substances, including the world's largest collection of:

• Organic compounds
• Inorganic compounds
• Metals
• Alloys
• Minerals
• Coordination compounds
• Organometallics
• Elements
• Isotopes
• Nuclear particles
• Proteins and nucleic acids
• Polymers
• Nonstructurable materials (UVCBs)

Approximately 15,000 new substances are added each day.

See the most up-to-date CAS REGISTRY figures.

Since CAS Registry Numbers are not dependent upon any system of chemical nomenclature, they can:

• Provide a reliable common link between the various nomenclature terms used to describe substances
• Serve as an international resource for chemical substance identifiers used by scientists, industry and regulatory bodies

Chemical compounds can be described in many different ways:

• Molecular formula
• Structure diagram
• Systematic names
• Generic names
• Proprietary or trade names
• Trivial names

A CAS Registry Number, however, is unique and specific to only one substance regardless of how many other ways the substance can be described.

Governmental agencies have found CAS Registry Numbers ideal for keeping track of substances because 

• They are unique
• They can be validated quickly and reliably
• They are internationally recognized

Find CAS Registry Numbers in:

• SciFinder^®
• STN^® databases
• CAS publications
• Other publications
  
  • Governmental regulatory agency commercial chemical inventories
  • Selected Elsevier databases
  • Handbooks, guides and technical reports
  • Other printed reference works
  • Chemical catalogs

In a hurry? Contact CAS Registry Number Lookup Service and ask for 24-hour turnaround (Mon-Fri).

Records in REGISTRY represent substances indexed for the CAS databases (CA^SM/CAplus^SM, CASREACT^®, CHEMCATS^®, CHEMLIST^®, MARPAT^®) and other databases in products such as SciFinder^® and STN^®.  Substances that come from sources other than literature or patent publications may not contain any references.  CAS indexes these substances to support registration policies, chemical libraries, chemical catalogs, web sources, reaction databases and data collections not represented in STN.

To learn more about a substance in REGISTRY that does not have any literature or patent references consult the Source of Registration (SR) and Class Identifier (CI) fields in STN.

While printed publications may contain outdated information, the CAS REGISTRY database is updated daily providing your best source for the latest CAS Registry Number information.

CAS is the source and final authority for CAS Registry Numbers. Other resources may have associated an incorrect CAS Registry Number with a compound, and use of that incorrect CAS Registry Number in searches could lead you to irrelevant or inappropriate information.