Somatostatin 5, 10, and 25 mug and saline were given as a 2 min bolus injection to 6 acromegalic patients in basal conditions. A significant dose-response relationship could be demonstrated between somatostatin and the suppressions of plasma growth hormone and insulin. The lowest somatostatin dose tested exerted a significant suppression of both hormones. Insulin suppression after the bolus injection lasted for 15 minutes, while the suppression of growth hormone was maintained for 30-50 minutes. In order to obtain total suppression of the elevated plasma growth hormone levels in acromegalics, 3 patients received 50, 250, and 500 mug of somatostatin as bolus injections at time 0, 90, and 180 minutes, 2 patients received 50 mug of somatostatin as bolus injections 4 times with an interval of 20 minutes between each injection, and finally 3 patients received a large dose of somatostatin, 3000 mug given as an infusion over 2 hours. The single injections of somatostatin were not followed by a satisfactory growth hormone suppression. In the infusion experiments, the average plasma growth hormone level was suppressed only 65%, resulting in individual plasma growth hormone plateaus of 20, 14, and 3.6 ng/ml. Only the lowest of these plateaus would be acceptable from a clinical point of view.