The effects of gestational age (GA), body weight, and prenatal exposure to betamethasone and indomethacin on the glomerular filtration rate (GFR) on d 3 of life in preterm infants were studied. GFR measurements were performed in 147 preterm infants with a GA between 23.4 and 37.0 wk by means of the continuous inulin infusion technique. Mean GFR values increased significantly with GA (r= 0.60,p< 0.001) and with body weight (r= 0.44,p< 0.001). Multivariate analysis indicated that GA was the most important determinant for this increase. Prenatal exposure to indomethacin resulted in significantly lower GFR values (-0.15 ± 0.03 mL/min,p< 0.001) at d 3 after birth. Prenatal administration of betamethasone and indomethacin significantly (p< 0.001) increased the GFR in comparison with exposure to indomethacin alone to levels not different than those seen in patients who were not prenatally exposed to betamethasone or indomethacin. GFR measurements were repeated in 40 preterm infants on d 10 after birth. During this 7-d period, a significant increase in GFR values (0.17 ± 0.03 mL/min,p< 0.001) was detected. This postnatal increase in GFR values was independent of GA and was not influenced by prenatal exposure to betamethasone or indomethacin. We conclude that prenatal exposure to betamethasone or indomethacin exerts significant effects on the renal function of preterm infants in the first days of life. (Pediatr Res36: 578–581, 1994)