This paper describes the content, organization, specifications, and methods of use of the CAS77 and CAS7276 online files of worldwide chemical literature, databases produced by Chemical Abstracts Service and available from System Development Corporation (SDC). The scope of the databases, their unit record, their data elements, their modes of subject searching, available user aids, and charges to users are detailed. Tables identify directly searchable data elements provided by SDC and database specifications for the CAS77 file. Figures illustrate samples of a unit record, a CHEMDEX file search, and a citation resulting from a search. (FM)