Objective: The authors evaluated the effect of implementing quality improvement (QI) programs for depression, relative to usual care, on primary care clinicians' knowledge about treatment. Design And Methods: Matched primary care clinics (46) from seven managed care organizations were randomized to usual care (mailed written guidelines only) versus one of two QI interventions. Self-report surveys assessed clinicians' knowledge of depression treatments prior to full implementation (June 1996 to March 1997) and 18 months later. The authors used an intent-to-treat analysis to examine intervention effects on change in knowledge, controlling for clinician and practice characteristics, and the nested design. Participants: One hundred eighty-one primary care clinicians. Interventions: The interventions included institutional commitment to QI, training local experts, clinician education, and training nurses for patient assessment and education. One intervention had resources for nurse follow-up on medication use (QI-meds) and the other had reduced copayment for therapy from trained, local therapists (QI-therapy). Results: Clinicians in the intervention group had greater increases compared with clinicians in the usual care group over 18 months in knowledge of psychotherapy (by 20% for QI-meds, P =.04 and by 33% for QI-therapy, P =.004), but there were no significant increases in medication knowledge. Significant increases in knowledge scores (P =.01) were demonstrated by QI-therapy clinicians but not clinicians in the QI-meds group. Clinicians were exposed to multiple intervention components. Conclusions: Dissemination of QI programs for depression in managed, primary care practices improved clinicians' treatment knowledge over 18 months, but breadth of learning was somewhat greater for a program that also included active collaboration with local therapists.