The document contains records of approximately 22,000chemicals which since 1970have been mentioned in a significant way in journals indexed in MEDLINE,the National Library of Medicines online bibliographic database. Originally housed in a manual card file these records were incorporated as a subset of the MEDLARS MeSH (Medical Subject Headings) file,and became searchable online in June 1980. The present list does not include any of the chemical descriptors that are to be found in the D Category of MeSH. The publication is intended to assist indexers,and the users of Index Medicus and MEDLINE. For the indexer,it provides more specific entries than those available in the printed MeSH. It permits users of Index Medicus to locate the chemical subject headings under which citations referring to a more specific chemical can be found.