In a randomized double-blind trial on antenatal corticosteroid treatment for the prevention of respiratory distress syndrome (RDS) a corticosteroid related beneficial effect was found. Possibly of more significance was the finding that the children born within 12 hours of their mother's admission to hospital showed a higher incidence of RDS than those born between 12 hours and one week after admission even in the placebo and untreated groups. Bèta-adrenergic drugs seemed to exert no other influence on the occurrence of RDS than can be explained by the delay of delivery. Prolonged ruptured membranes appeared to decrease the incidence of RDS to the same extent as other symptoms of threatened preterm labour.