Despite widely publicized hypertension treatment guidelines for physicians and lifestyle recommendations for patients, blood pressure control rates remain low. In community-based primary care clinics, we performed a nested, 2 x 2 randomized, controlled trial of physician intervention versus control and/or patient intervention versus control. Physician intervention included internet-based training, self-monitoring, and quarterly feedback reports. Patient intervention included 20 weekly group sessions followed by 12 monthly telephone counseling contacts and focused on weight loss, Dietary Approaches to Stop Hypertension dietary pattern, exercise, and reduced sodium intake. The primary outcome was change in systolic blood pressure at 6 months. Eight primary care practices (32 physicians) were randomized to physician intervention or control groups. Within those practices, 574 patients were randomized to patient intervention or control groups. Patient mean age was 60 years, 61% were women, and 37% were black. Blood pressure data were available for 91% of patients at 6 months. The main effect of physician intervention on systolic blood pressure at 6 months, adjusted for baseline pressure, was 0.3 mm Hg (95% CI: 1.5 to 2.2; P=0.72). The main effect of the patient intervention was 2.6 mm Hg (95% CI: 4.4 to 0.7; P=0.01). The interaction of the 2 interventions was significant (P=0.03); the largest impact was observed with the combination of physician and patient intervention (9.7 +/- 12.7 mm Hg). Differences between treatment groups did not persist at 18 months. Combined physician and patient interventions lowers blood pressure; future research should focus on enhancing effectiveness and sustainability of these interventions.