To elucidate factors determining the development of left ventricular hypertrophy, we performed measurements of intraerythrocyte sodium and intraplatelet calcium concentrations, measurements of plasma and urinary catecholamine levels and plasma renin activity, calculation of left ventricular mass using echocardiography, and 24-h ambulatory blood pressure (BP) monitoring. The results indicate that abnormalities of sodium and calcium mobilization may play an important role in the adaptation of left ventricular muscle to a persistent increase in BP.