A double-blind controlled study on the prenatal use of betamethasone in the prevention of respiratory distress syndrome (RDS) was carried out on 137 patients from 24 to 34 weeks' gestation. The incidence of RDS was less in the treated group (5%) than in control group (17%). The neonatal mortality rate was lower in the treated group (5%) than in the control group (18%) due to an excess of neonatal deaths in the placebo group.