We carried out a controlled trial of teaching the critical appraisal of clinical literature among final-year clinical clerks. Tutors at two of four teaching hospitals were offered a short course in the critical appraisal of clinical articles that describe diagnostic tests and treatments and were assisted in identifying and appraising specialty-specific articles that described those diagnostic tests and treatments that clinical clerks were sure to encounter during their clerkship tutorials. Tutors and clerks at the other two hospitals received no special intervention and served as controls. Experimental and control clinical clerks completed pretests and posttests of their ability to take and defend a stand on whether to apply specific diagnostic tests and treatments in specific clinical situations. Experimental clerks demonstrated both statistically and "clinically" significant increases in their critical appraisal skills, improving 37% on the diagnostic test exercise and 8% on the treatment exercise; control students' scores deteriorated for both.