In an investigation in 1967 of about 100 male twin pairs collected from the Swedish Twin Register, discordance with respect to the presence of CHD was found in 37 pairs of which 19 were MZ. The investigation included physical examination, cholesterol measurements, and an interview regarding, among other things, smoking habits. In a follow-up study in 1974 — seven years after the original investigation — all but one of the 37 twins regarded in 1967 as free from overt CHD could be traced. Ten of the 36 twins had developed symptoms of overt CHD (angina pectoris or infarction); 18 twins were still healthy, 2 had died from other causes, and 6 had questionable complaints of breast pains. In a comparison of the two groups of twins with and without symptoms of overt CHD, no differences were found with respect to blood pressure, serum cholesterol, or smoking habits, as presented at the 1967 investigation. It is concluded that none of these factors seemed to influence the future development of CHD in twins apparently tainted with a heredity for this disease.