The study was undertaken to obtain simultaneous measurements of circulating anterior pituitary hormone levels after the i.v. injection of arginine-vasopressin (AVP). Nine healthy men, mean age 31 years (range 24-41), received single blind with at least one week apart, after resting in the supine position for 30 min, AVP 0.26 microgram/kg body weight i.v. (Pitressin, Parke-Davis) or saline in randomized order. Blood samples were taken at 0, 10, 20, 30, 45 and 60 min for analyses of serum or plasma levels of ACTH, prolactin, TSH, GH, FSH, LH and AVP. The hormone responses after AVP or saline were calculated as the area under the curve (AUC) 0-60 min as well as the change in hormone levels from 0 to 10 min to pick up possible short lasting effects when there was no significant difference in AUC between AVP and control. As expected the highest plasma concentration of AVP was measured 10 min after the injection of AVP and well comparable to those in other studies where AVP was observed to release ACTH. The AUC:s for both ACTH and prolactin levels were significantly increased after AVP in comparison with saline (p = 0.008 and p = 0.038, respectively). The AUC:s for the other hormones measured were not significantly changed after AVP, but there were small but significant changes in the 0-10 min values for TSH and LH after AVP compared to saline. It is concluded that AVP has the potency to release not only ACTH but also prolactin in healthy men.