Blood pressure (BP), heart rate (HR), height, weight, hereditary factors, smoking habits and physical activity have been determined in a random population sample of men aged 47-54 years attending a screening examination, which was part of a multifactor primary preventive trial. Of the 9,967 men who were invited to the study, 83% answered a postal questionnaire and 75% took part in the screening examination. Of all persons not on antihypertensive treatment, 10% had systolic blood pressure (SBP) greater than 175 mmHg and 6% had diastolic blood pressure (DBP) greater than 115 mmHg. Of those on hypotensive treatment 43% had SBP greater than 175 mmHg and 30% had DBP greater than 115 mmHg, indicating that the hypertension was not well controlled. A weak positive correlation was found between HR and BP and between relative body weight (RBW) (defined as [weight/height] - 100) and BP. Both HR and RBW were higher in the treated hypertensives than in the remainder of the population studied. Subjects with a positive heredity for myocardial infarction or stroke had a significantly higher BP than persons with a negative heredity, but the absolute differences were small. A weak relationship was demonstrated between smoking habits and DBP, with the lowest BP in persons smoking greater than 25 cigarettes a day. There was no relationship between the degree of physical activity and BP.