PURPOSE. To assess time use by students during clinic sessions of an ambulatory care clerkship. METHOD. All 207 third-year students at the Medical College of Wisconsin during 1991–92 were asked to report their time use in eight categories during two clinic sessions of the three-week clinical component of the required clerkship in ambulatory care medicine. Other variables assessed were site of clinical rotation, first versus third week of rotation, and time of year of rotation. The statistical methods used were t-tests and one-way analysis of variance. RESULTS. Of the 207 students, 192 (93%) completed time-allocation reports for the first and third weeks of their rotations. The average time spent per clinic session was four hours. Compared with the students at faculty practice sites, the students at private practice sites spent significantly more time observing and working with preceptors as they saw patients and significantly less time doing solo clinical work (reviewing and writing in charts). During the course of each rotation, the students increased the time they saw patients by themselves and decreased the time they observed preceptors. As the year progressed, later cohorts of students spent less time observing preceptors and more time working by themselves. CONCLUSION. Both within and across rotations, the students eventually spent less time observing and more time working independently. However, the results suggest that preceptors in private practice may not allow students as much autonomy as do faculty preceptors. Further research is needed to determine (1) whether the differences between types of preceptors result in meaningful differences in the quality of education and (2) which activities or mixes of activities contribute most to students' education.