Infusions of Citrullus colocynthis Schrad. (Cucurbitaceae) fruits are traditionally used as antidiabetic medication in Mediterranean countries, but to our knowledge no studies have been undertaken so far to determine the possible mechanisms involved in the antidiabetic properties of the fruit. The present study was designed to investigate whether these fruits possess insulinotropic effects. For this purpose, different extracts of Citrullus colocynthis seed components were obtained: RN II (crude extract), RN VI (hydro-alcoholic extract), RN X (purified extract) and RN XVII (beta-pyrazol-1-ylalanine), the major free amino acid present in the seeds. The insulin secretory effects of these different extracts were evaluated in vitro in the isolated rat pancreas and isolated rat islets in the presence of 8.3 mM glucose. All tested extracts, when perfused for 20 min at 0.1 mg/ml, immediately and significantly stimulated insulin secretion. This effect was transient. In addition, the purified extract (RN X) provoked a clear dose-dependent increase in insulin release from isolated islets. Moreover, a significant and persistant increase in pancreatic flow rate appeared during RN VI, RN X and RN XVII perfusions. In conclusion, our results show that different Citrullus colocynthis seed extracts have an insulinotropic effect which could at least partially account for the antidiabetic activities of these fruits.