To investigate the usefulness of stress testing for the evaluation of hypertensive heart disease, 40 subjects, 28 men and 12 women (mean age 30.8 ± 6.2 years), with mild or moderate hypertension, without ST segment or T wave abnormalities in their resting ECG, were examined. 13 patients (32.5%) showed exercise-induced ST segment depression. The heart rate at rest was significantly higher in the patients with a positive response; 6 of the 7 subjects with electrocardiographic signs of left ventricular hypertrophy (summed SV<sub>1 </sub>+ maximum R V<sub>5</sub>/V<sub>6</sub> voltage of 45 mm or more) had a positive exercise electrocardiographic test. There were no significant differences between positive and negative cases in age, sex, systolic and diastolic blood pressure, or the double product (heart rate × systolic pressure) at rest or during exercise. After resting blood pressure values had been significantly decreased by giving methyldopa with or without diuretics for at least 6 months, there were a regression of left ventricular hypertrophy in the resting ECG and an impressive reduction in the prevalence of exercise-positive responses (to 17.5%). In the 7 patients with positive exercise electrocardiographic tests even after antihypertensive treatment, no significant reduction in blood pressure values during exercise was obtained.