Antepartum administration of aminophylline (AF) to pregnant animals resulted in accelerated and increased pulmonary maturation as well as in decreased morbidity and mortality from RDS in premature offspring. The present study was undertaken to evaluate the effect of antenatal AF treatment on the frequency of RDS among premature infants born of women who were treated (18) and to compare this group with betamethasone (GC) treated group (16 women). No statistical significant differences were noted between the AF and GC groups in the incidence of RDS (AF = 11.0%; GC = 0%) and in the frequency of perinatal deaths (AF and GC = 0%). Only a significant difference was noted between the AF group and the GC group in the incidence of neonatal signs of infection (AF = 0%; GC = 50%). The authors conclude that antenatal AF treatment may be as effective as GC in the prevention of RDS in premature infants with, for the moment, no side effects.