The file aims at broad, rapid coverage of reactions coupled with specialized search software that enables users to focus their searches. More than one million reactions from over 65 000 documents are accessible through CASREACT. Interaction with the CAS Registry File and graphic displays aid both searching and interpretation of CASREACT information.This paper begins with a discussion of reaction information in the CA File and the origins of CASREACT. It then focuses on CASREACT as it exists today in terms of content and coverage, search features, the various display options for viewing the reaction information, and other general capabilities of the file. It also discusses user feedback with regard to CASREACT and actions taken or being planned as a result of that feedback. REACTION INFORMATION IN THE CA FILEThe reaction information in the CA File falls into three categories: (1) terms from the title, abstracts, and keywords;(2) compounds indexed and the text associated with them; and(3) controlled vocabulary index terms, particularly reaction terms. Title, abstract, and/or keyword terms always reflect the terminology used by the author; keywords may also include standardized terms. The use of controlled vocabulary terms is based on the author's emphasis shown in the title, abstract, and full text of the document.Compounds are indexed by their CAS Registry Number(RN) with either a simple text 'prepn. of or additional words showing preparation, properties, and/or uses for a product. This information is combined with a number of synonyms for 'prepared' (in context) to algorithmicly associate the searchable suffix 'P' with CAS Registry Numbers (e.g., 1234-56-7P). This pointer makes the retrieval of prepared compounds straightforward in the CA File. CAS has indexed starting materials routinely since 1976. Reactants are associated with 'reaction of and other reaction-type terms. When a compound is both prepared and further reacted, the text shows both ideas, e.g., 'preparation and reaction of, with ...'. This type of text allows the proper assignment of the 'P' and shows the further reaction.Generally, only reactants and products are indexed for the CA File. Author emphasis occasionally will cause reagents and (more rarely) solvents to be indexed as well. Catalysts which are prepared are always indexed, but the common catalysts arc indexed only as a result of author emphasis. Text terms with any of these reaction participants will make their role obvious.Controlled vocabulary terms-general subject terms in printed Chemical Abstracts (CA)-are hierarchically assigned for CA, with the most specific term being chosen for input.Thus, named reaction terms, if they have been selected as

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