To investigate the involvement of the sympathetic nervous system and cell membrane sodium transport in hypertensive cardiac hypertrophy, we divided 51 middle-aged male patients with essential hypertension into cardiac hypertrophy and noncardiac hypertrophy groups. We then compared the plasma noradrenaline concentration after exercise, the cardiovascular response to exercise and sympathomimetic agents, and cell membrane sodium transport in the two groups. There were differences between the cardiac hypertrophy and noncardiac hypertrophy groups with regard to the pressor response to exercise and noradrenaline (i.e. the response to sympathetic alpha-receptor stimulation) as well as the intracellular sodium concentration and cell membrane sodium transport. We concluded that there were abnormalities of the pressor response to alpha-receptor stimulation and of intracellular sodium concentration and cell membrane sodium transport in patients with hypertension and cardiac hypertrophy. These abnormalities might play some role in the pathogenesis of hypertensive cardiac hypertrophy.