We measured the ability of CCK-8 alone, a test meal alone, or a combination of the two, to increase peripheral plasma somatostatin levels in the baboon. Baboons received a five-minute intravenous infusion of either CCK-8 (1, 2, or 4 micrograms/kg) or saline prior to a 30-minute meal. CCK-8 administration at all doses resulted in a significant rise of plasma somatostatin-like immunoreactivity (SLI). In addition, ingestion of a meal following a control saline infusion resulted in a significant rise of plasma SLI. However, the meal-related rise in SLI was blunted by prior administration of CCK-8 at all doses, including a dose which did not significantly decrease meal size. CCK-8 administration at all doses also blunted the meal-related rise of plasma insulin and glucose. We conclude that the known ability of CCK-8 to inhibit gastric emptying, as well as to decrease meal size, may account for its suppression of the meal-related SLI release.