If two consecutive glucose infusions are administered with 40 min of rest between, the insulin response to the second challenge is markedly potentiated. When the insulin response to the first glucose infusion was suppressed by 65% with the aid of adrenaline, potentiation of the insulin response to the second infusion was not modified. This suggests that the generation of a state of enhancement in the islet does not necessitate that glucose exerts its insulin releasing action. It is postulated that islet glucose metabolism may be involved in producing the potentiation. Pretreatment of the subjects with a glucose infusion enhanced also the insulin responses to glucagon and to tolbutamide, given intravenously 50 min later. Thus, the potentiation generated by glucose is not restricted to the insulinogenic signal induced by glucose. The eventual role that the beta-cell adenylate cyclase may play in this respect is discussed.