1. In 16 borderline and 18 sustained hypertensive patients, interventricular septal thicknesses (by echocardiography) were greater than those found in 18 healthy subjects. Values in borderline and sustained hypertensives did not differ significantly.
2. In healthy subjects and borderline hypertensive patients, posterior wall thicknesses were normal, whereas they were greater in sustained hypertensive patients than in the former two groups.
3. In borderline hypertension, interventricular septal thickness was positively correlated with resting supine (r = 0.89, P < 0.001) as well as upright (r = 0.60, P < 0.01) plasma noradrenaline, but not with adrenaline, plasma renin activity and mean blood pressure.
4. In sustained hypertension, posterior wall thickness was positively correlated with mean blood pressure (r = 0.85, P < 0.001), but not with noradrenaline, adrenaline and plasma renin activity.
5. In human hypertension, left ventricular hypertrophy seems to involve only the interventricular septum in the borderline stage, extending to the posterior wall in the sustained stage. Adrenergic overactivity could play an important role in development of interventricular septal hypertrophy in borderline hypertension, whereas pressor factors could be mainly involved in the development of posterior wall hypertrophy in sustained hypertension.