Our objective was to determine whether an educational intervention and prompting intervention for physicians improved dietary counseling of patients with high blood cholesterol and resulted in beneficial changes in patients' diets and cholesterol levels. We instituted a factorial design, multicenter, randomized, placebo-controlled trial to test two interventions. We tested the trial at continuity care clinics of internal medicine residents at seven community and university medical centers in the northern and eastern United States. Our participants were 130 internal medicine residents and 254 adult outpatients with blood cholesterol levels of 240-300 mg/dL. Interventions included an educational program for resident physicians designed to improve their skills and confidence in dietary counseling (two one-hour sessions with specially prepared printed materials for use in counseling) and a prompting intervention, which was a fingerstick blood cholesterol determination prior to the patient's clinic visit. Resident physicians' knowledge, attitudes, and self-reported behaviors were assessed prior to the intervention and 10 months later using chart audits and questionnaires. Residents' behaviors were also assessed by exit interviews with patients. Patients' knowledge, attitudes, behaviors, and fingerstick blood cholesterol levels were measured at baseline and 10 months later. The educational program increased the percentage of physicians who were confident in providing effective dietary counseling (baseline of 26% to 67%-78%; P < .01). The prompting intervention approximately doubled the frequency of physician counseling (P = .0005) and increased the likelihood that patients would try to change their diets. When both interventions were combined, most outcomes were better, although not statistically significant. Cholesterol levels, however, decreased only marginally and were no different among groups at 10-month follow-up. Despite success in changing physicians' attitudes and behaviors and increasing patients' willingness to change their diets, there was no significant change in patients' cholesterol levels. Medical Subject Headings (MeSH): randomized controlled trial; cholesterol; patient education; behavior therapy; education, medical; diet.