Dexamethasone or saline was administered in a randomized fashion to pregnant Macaca nemestrina for 3 days prior to preterm abdominal delivery. The steroid-treated animals demonstrated a greater hemoglobin concentration and a greater mean corpuscular hemoglobin concentration in cord blood. There was no difference between the groups in mean P50 in cord blood. The infants of steroid-treated animals had less frequent and less severe hyaline membrane disease. We conclude that antenatal steroid administration ameliorates postnatal respiratory distress without inducing changes in P50 and with only a small change induced in cord blood hemoglobin.