CAS CAS Registry Number

50-00-0 in cas

62-53-3 in cas

9999* in cas

The CAS field lists one or more hyphenated numbers that identify the chemical substance(s) cited in the original document. Each number, assigned by the Chemical Abstracts Service, is unique and is in the format: XXXXXX-XX-X. Include all hyphens when searching for CAS Registry Numbers. Any collection of substances, such as "sulfonic acids," "ions," "proteins," is represented by "0" in this field. The corresponding textual name of a substance or collection of substances is listed in the Prime Name of Substance (PN) field.

Browsing CAS Registry Numbers

As an alternative to searching with the field label, you can browse numbers and search for them directly from the CAS Registry Number Index Field-Specific Index. This field-specific index contains only CAS Registry Numbers available in the database. Results of a search in this index display in the CAS field.

Searching for EC and CAS Numbers Simultaneously

You can search for the numeric identification for enzymes and chemical substances simultaneously using a special pseudo field. The CAS Registry Number or EC Number (RN) field enables you to search in the CAS and EC Number (EC) fields simultaneously. Search results display in the respective fields.