Renal function was measured in seven premature lambs delivered spontaneously after a fetal injection of betamethasone, four near term lambs delivered via cesarean section after a fetal injection of a placebo and in ten spontaneously delivered full term lambs. Glomerular filtration rates were significantly higher in the premature betamethasone treated than in the near term placebo treated and the full term lambs. Fractional sodium excretions were significantly lower in the betamethasone treated preterm than the placebo treated near term lambs. This suggests that glucocorticoid accelerates renal glomerular and possibly tubular maturation. As in the lung, fetal administration of glucocorticoid stimulates functional maturation of the kidney.