ECG findings indicating significant left axis deviation and tall R waves (left type) according to the Minnesota Code have been investigated in 4210 subjects of both sexes aged 35-54. The changes were analysed twice over a period of three years. Left axis deviation was seen in 2.9%. It was least frequent in the youngest subjects and occurred 2.5 times more often in men than in women. The prevalence of tall R waves was 2.2%. It also was least frequently seen in the youngest subjects and was two times more common in men than in women. This finding was significantly connected with changes in the S-T segment and T waves at rest or after exercise. However, as many as 66% of the subjects with tall R waves had no S-T segment or T wave changes. Both left axis deviation and tall R waves were significantly associated with combined diastolic-systolic hypertension. Left axis deviation was fairly stable. Tall R waves were persistent in only one third of the subjects, reflecting the dynamics of the myocardium. It was more often seen in connection with signs of myocardial ischemia.