OBJECTIVE To determine whether a workshop on medical ethics attended by family medicine preceptors would affect their students' learning of ethics, and what educational and experiential factors affected the students' learning about ethics. METHODS A 3-hour workshop planned by a group of family physicians and ethicists and taught by a faculty member and an ethicist was offered to family physician preceptors. Students entering the clerkship were invited by letter to complete written answers to two clinical papers. Their answers were compared with "ideal" answers based on a weighted composite of the responses of 12 family physicians with a particular interest in ethics. The scores of students assigned to preceptors who had been offered the workshop were compared with those of students assigned to a control group of preceptors. Clerks were also asked about influences on their answers. METHODS The 86 preceptors participating in the family medicine programs at the University of Western Ontario, divided by random selection within geographic clustering into an experimental group of 50 and a control group of 36. Preceptors offered the workshop were considered to be in the experimental group whether or not they attended. The student questionnaire was sent to all students entering the family medicine clerkship program in the academic year 1989-1990 and some in the following year, until sufficient responses were received. Responses were analyzed from 32 clerks in the experimental group and 36 in the control group. METHODS Performance of students whose preceptors were invited to the workshop against performance of students whose preceptors were not invited to the workshop. RESULTS No significant differences were noted between the performance of students whose preceptors were offered the workshop and those whose preceptors were not. CONCLUSIONS The single outcome measure and the volunteer bias make conclusions difficult to draw. Further studies varying interventions and outcome measures are warranted.