To measure the effects of a collaborative care model that emphasized the role of clinical pharmacists in providing drug therapy management and treatment follow-up to patients with depression, we conducted a randomized controlled trial at a staff model health maintenance organization. We compared the outcomes of subjects treated in this collaborative care model (75 patients, intervention group) with subjects receiving usual care (50 patients, control group). After 6 months, the intervention group demonstrated a significantly higher drug adherence rate than that of the control group (67% vs 48%, odds ratio 2.17, 95% confidence interval 1.04-4.51, p=0.038). Patient satisfaction was significantly greater among members randomly assigned to pharmacists' services than among controls, and provider satisfaction surveys revealed high approval rates as well. Changes in resource utilization were favorable for the intervention group, but differences from the control group did not achieve statistical significance. Clinical improvement was noted in both groups, but the difference was not significant. Clinical pharmacists had a favorable effect on multiple aspects of patient care. Future studies of this model in other health care settings appear warranted.