Prostaglandin E1 (PGE1) was infused directly to the autotransplanted adrenal gland of the Na deficient sheep, for either 15 or 60 min, at a rate to give a concentration of either 2 or 20 ng/ml adrenal arterial blood. In all experiments infusion of PGE1 was followed by a sustained increase in adrenal blood flow; in one third (n = 7) a marked fall in aldosterone secretion rate was seen; in the remainder only slight changes in aldosterone secretion rate. No factor —age, sex, initial levels of steroidogenesis, degree of vasodilatation—appeared to be able to be correlated with either type of response. For the experiments as a whole, the fall in ASR was statistically significant (p<.02, 2-tailed t-test); cortisol and corticosterone secretion rates both showed mean rises, but in neither case to significant levels (p>.05). Such variability in results would suggest caution in assigning a particular role to the prostaglandins in adrenal steroidogenesis. (Endocrinology88: 367, 1971).