Background: Antenatal corticosteroid therapy is of great benefit to preterm infants, owing largely to effects on lung maturation. In sheep, repeated betamethasone injections given to the ewe improve lung function following preterm birth but also cause intrauterine growth restriction (IUGR). In humans and in animal models, IUGR is associated with impaired postnatal lung function. The effects on lung function of repeated prenatal betamethasone treatments and associated IUGR following term delivery are unknown. Aim and study design: To determine the effects of antenatal betamethasone treatments on postnatal arterial pressure, blood gases, ventilation, pulmonary gas volumes and compliance in serial studies of four groups of lambs until 4 weeks of age. Subjects: Treatment groups were (1) maternal injections of saline at 104, 111 and 118 days of gestation, (2) a single maternal injection of betamethasone (0.5 mg/kg) at 104 days followed by saline at 111 and 118 days, (3) repeated betamethasone injections at 104, 111 and 118 days, or (4) no intervention (term is similar to150 days). Results: Repeated maternal betamethasone injections reduced birthweight and resulted in reduced postnatal body weights and arterial pressure throughout the first postnatal month. Lung function was not deleteriously affected by single or repeated maternal betamethasone treatments: blood gases, minute ventilation, lung volumes and compliance were not different between groups of lambs. Conclusions: The absence of alterations in postnatal blood gases contrasts with other models of IUGR in sheep and suggests that changes in lung structure caused by betamethasone may benefit IUGR neonates born at term. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.