The infusion of natural somatostatin (SRIF) has been able to partially correct postprandial hyperglycemic reactions in insulin-dependent diabetes mellitus (IDDM). SMS 201-995 (Sandostatin) is a long-acting derivative with a growth hormone-suppressive effect 10-60 times more potent than the native peptide. The effect of SMS 201-995 (50 µg s.c.) on glucose control by exogenous insulin has been documented in a series of type I diabetics after stabilization of blood sugar by an artificial pancreas. Inhibition of counterregulatory mechanisms significantly diminished the postprandial hyperglycemia, and insulin requirements, both total and 2 h after meals, were markedly decreased. Also the effect of a single s.c. injection of 100 µg SMS 201-995 on the dawn phenomenon in a patient with poorly adjustable diabetes was investigated. The glucose escape observed during the control night was blocked by SMS 201-995. Thus, the stabilizing action of this peptide on postprandial and nocturnal hyperglycemia in unstable diabetes warrants further studies.