Results of a study comparing the performance of the Colleague and PaperChase computer systems, designed for searching of the National Library of Medicine's MEDLINE database of biomedical references, are presented. Two matched groups of second-year medical students each received three hours of instruction, one group in Colleague, the other in PaperChase. Each student then attempted ten test searches. The next day the groups were reversed, and each student attempted five additional searches. During the 3.5 hours allocated for searching, users of Colleague attempted 64 test searches and retrieved 376 target references: users of PaperChase attempted 78 searches and retrieved 496. Users of Colleague took a mean of 2.2 minutes and spent a mean of $1.20 to find each target reference: users of PaperChase took 1.6 minutes and spent $0.92. The authors conclude that after limited training, medical students find more references faster and at lower cost with PaperChase than with Colleague.