A controlled trial of antepartum glucocorticoid treatment for prevention of Respiratory Distress Syndrome (RDS) or Hyaline Membrane Syndrome (HMS) was carried out. 91 mothers, in whom premature delivery threatened between 27 and 37 weeks of gestation, were given intramuscular injections of 8-12 mg of betamethasone as well as medication inhibiting uterine activity (tocolytica and sedation) and strict bedrest to delay premature delivery for at least 24 to 48 hours. A control group of 118 mothers, who were hospitalized late and premature delivery could not be delayed, had no betamethasone treatment. There was no significant differerence in the incidence of Respiratory Distress Syndrome in premature infants in both groups, but there was a 50% lower mortality rate of Respiratory Distress Syndrome in the betamethasone treated group, due to a milder course of Respiratory Distress Syndrome Disease. Harmful effects from corticosteroids given to pregnant women prior to premature delivery were not observed in our group. The prophylactic treatment with betamethasone to diminish the mortality rate of Respiratory Distress Syndrome is therefore considered encouraging and profitable.