We examined 87 men with moderate hypertension (diastolic blood pressure, DPB, greater than or equal to 95 and less than 110 mmHg) (mean age 45, range 22-64, years) with echocardiography and maximal ergometer bicycle test. Left ventricular mass index (LVMI) was calculated according to the Penn convention. Mean LVMI was 126 (60-210) g/m2. The maximal systolic blood pressure (SBP) during exercise was on average 217 (155-260) mmHg. Linear regression analysis revealed a significant correlation between LVMI and SBP at rest (r = 0.48, P less than 0.001) and during exercise (r = 0.39, P less than 0.001). Multiple regression analysis correcting for differences in age, cumulative work and cholesterol level revealed a significant correlation between LVMI and SBP at rest (t = 4.07, P less than 0.0001) and during exercise (t = 3.25, P = 0.002). Thus in patients with established, moderate hypertension exercise SBP is not more predictable for LVMI than is SBP at rest.