In order to study what characteristics accompany the development of pregnancy-induced hypertension (PIH) and what parameters, if any, differentiate hypertension alone from hypertension with proteinuria, we evaluated 119 women with PIH who had hypertension alone, 73 women with PIH who had hypertension and proteinuria ⩾ 0.3 g/l, 63 women with normal pregnancy, 20 normal non-pregnant women. In comparison with normal pregnant women and normal non-pregnant women, women with PIH showed an increase in heart rate, suggesting an increased peripheral sympathetic tone, and an initial derangement in renal function as shown by the increase in serum uric acid and reduction in sodium excretion and total and fractional calcium excretion at any given level of sodium excretion. These changes were more marked in patients with hypertension and proteinuria. Higher levels of systol ic blood pressure (SBP) were present in women with hypertension alone who subsequently developed proteinuria, conipat-ed with those who had only hypertension until term. According to our data hypertension alone and hypertension with proteinur-ia seem to be two aspects of on1y differing severity of the same disease