Summary: We have examined the effect on lung liquid secretion of catecholamines infused in chronically catheterized fetal lambs in utero. Isoproterenol and epinephrine inhibited secretion, an effect which increased with gestation and, in fetuses near delivery, caused absorption of lung liquid. In 7 out of 8 experiments nor-epinephrine had no effect on secretion. This pattern of response and the fact that the inhibitory effect could be blocked by propranolol indicate a mode of action involving β-adrenergic receptors. Speculation: The observed effects on lung liquid secretion were achieved with infusion rates of epinephrine which are well within the range for endogenous production by the adrenals in response to splanchnic nerve stimulation or asphyxia. Thus the marked increase in the secretion of epinephrine which occurs during parturition may be an important factor in initiating lung liquid absorption. Permanent inhibition of lung liquid secretion postnatally may be due to greater sensitivity of the pulmonary epithelium to β-adrenergic stimulation and to the higher “resting” output of epinephrine from the adrenals of neonates compared with fetuses.