This report describes PaperChase, a computer program that permits users to search medical literature by author's name, journal of publication, title word, or medical subject heading (MeSH term), as indexed by the National Library of Medicine. PaperChase was installed in the medical library of Beth Israel Hospital in Boston, with a data base of 400,000 references--nearly all the articles shelved there. During the first year of operation, 1032 medical students, house officers, practicing physicians, and other library users, without formal instruction or user's manual, conducted 8459 searches and displayed 399,821 references, 97,769 of which they selected for printing. Among users who conducted an initial search, 49 per cent returned to complete five or more searches, and 14 per cent returned to complete 20 or more. The large number of satisfied users and the low installation and operating costs suggest that PaperChase could be a valuable means of providing widespread computerized bibliographic retrieval.