Pregnant rats received propranolol (5 or 10 mg/kg/day) from day 10 of gestation; controls were untreated. Lung wet:dry weight ratios were increased in treated fetuses delivered by hysterotomy at day 21 ; no difference was seen at birth after vaginal delivery. On subsequent days, treated pups exhibited higher wet:dry weight ratios, implying impaired postnatal lung water clearance. Surfactant pools were decreased proportionately at both doses. Ongoing surfactant synthesis was unaffected at either dose. Baseline secretion was reduced for those exposed to 10 mg/kg/day. Secretory response to beta-agonist stimulation was impaired in both treatment groups. Chronic beta-blockade alters fetal lung water clearance, surfactant stores, and secretory response to beta-agonists.