The effects of arginine vasopressin (AVP) and epinephrine on lung liquid secretion were investigated in 67 acute fetal goats (116 days of gestation to term) with intact umbilical cords after caesarean section. Secretion was measured by an impermeant tracer technique. AVP was infused intravenously (1.6-39.2 mU/(kg.min); 2 h) into 26 fetuses. All fetuses below 130 days of gestation, except one, showed no response. All above 133 days reduced secretion, or turned to reabsorption, except at the lowest infusion rate. The effect persisted, and usually increased postinfusion. Expansion of the lungs with saline did not change the response. The percentage reductions were linearly related to the logarithm of the infusion rate (threshold, 1.42 mU/(kg.min]. The absolute reductions were linearly related to fetal weight. Epinephrine was infused intravenously (0.30-6.72 micrograms/(kg.min); 1-2 h) into 12 fetuses. All fetuses (118 days to term) reduced secretion or reabsorbed by the second hour. At the highest infusion rate, reabsorption was immediate; at the lowest, secretion increased slightly, then fell significantly in the second hour. Epinephrine acted at levels considered physiological at delivery in the sheep. AVP appears to act at plasma levels found in most vaginal deliveries; it may augment epinephrine-induced reabsorption during stress, and help long-term removal of lung fluid.