The postprandial secretion of insulin, gastrin and somatostatin was studied in 23 extremely obese subjects and nine normal-weight controls after a liquid test meal. Apart from a significantly higher insulin level in the obese group, no significant intergroup difference was found. The effect of weight loss on the same hormones was studied in 18 patients 6 months after gastric banding. The mean weight loss during this period was 33 +/- 2.1 (SEM) kg. There was significant decrease in postprandial insulin secretion after gastric banding, but neither gastrin nor somatostatin levels were altered.