Blood pressure (BP) readings in the doctor's office are frequently higher than home or ambulatory values. This study examines the role of the physician in the aetiology of the 'white coat' effect, by comparing standard readings taken by the family physician of 27 treated hypertensive patients with readings taken by an automated BP recording device, with the patient alone in the examining room during the same office visit. The physician and automated readings were each compared to the mean awake ambulatory BP. Mean (+/-s.e.m.) routine office BP (mm Hg) recorded by the patient's physician (155+/-4/80+/-2) was similar to the mean value obtained using the automated BP recording device (157+/-3/83+/-2). The mean awake ambulatory BP was 145+/-3/78+/-2 with the systolic value lower (P < 0.05) than either the physician or automated reading. Self-measurement of BP by the patient in the office setting does not reduce the magnitude of the white coat effect.