The mass of left ventricular (LV) muscle plays a central role in hypertension. Echocardiographic LV mass has been shown to reflect the level of blood pressure over time, obesity, diet, and other factors, and to serve as the strongest predictor yet discovered, other than advancing age, of cardiac complications of hypertension. Recent research suggests, in addition, that individuals destined to become hypertensive have increased LV mass before hypertension becomes clinically apparent. Several published studies have compared LV mass in groups of normotensive children to young adults considered to be at high or low genetic risk of hypertension based on the presence or absence of hypertension in their parents. In each instance LV mass was higher in the offspring of hypertensive parents and this difference exceeded that expected for small differences in body habitus or arterial pressure. A longitudinal study in children also showed that LV mass predicted subsequent blood pressure level. We recently performed a study of 132 initially normotensive employed adults, 15 (11%) of whom developed borderline hypertension during a 5-year follow-up. The development of hypertension was not predicted by subject age, body habitus, blood pressure, or a variety of biochemical measurements. The only baseline measurement that predicted development of hypertension was that of LV mass (92 +/- 25 v 77 +/- 19 g/m2, P less than .005), and the likelihood of developing hypertension increased progressively from 3% in the lowest quartile of LV mass of 24% in the highest quartile.(ABSTRACT TRUNCATED AT 250 WORDS)