A group of 412 infants with birthweights between 501 and 2500 g and gestational ages of 36 wk or less were studied for the influence of both prolonged rupture of amniotic membranes and maternal hypertension on the incidence of idiopathic respiratory distress syndrome (IRDS). The occurrence of these complications was associated with a significant decrease in the incidence of IRDS only in infants with birthweights between 1501-2500 g (37.4% in the no complications group vs. 12.8% in the complications group; P < .01) or gestational ages of 33-36 wk (35.2% in the no complications group vs. 13.1% in the complications group; P < .01). In infants with birthweights of 1500 g or less or gestational ages of 32 wk or less, the specific antecedent complications of pregnancy did not alter the incidence of IRDS. Rupture of the membranes for more than 72 h had no greater effect on the incidence of IRDS than those lasting 24-72 h.