We studied the effects of a premeal sc injection of an analog of somatostatin (SMS 201-995, Sandoz) on the postprandial glycemic excursions, insulin requirement and hormone profiles (GH, glucagon and C-peptide) in 8 IDDM patients (diabetes duration 14.0 +/- 6.5 yr, daily insulin requirement 36 +/- 6.4 U) maintained normoglycemic by connecting them to a closed-loop insulin infusion system (Betalike, Genoa). The morning of the test the patients were connected to the Betalike and their glucose levels stabilized for at least 4 h. At 13:00 h the study was begun with a sc injection of 50 micrograms of SMS 201-995 or placebo (randomly) and a standardized mixed meal (800 Kcal) was given. Blood samples were obtained 0, 15, 30, 60, 120 and 180 min after the injection. Each patient was tested both with SMS 201-995 and placebo. Postmeal glycemic peaks were decreased after SMS 201-995 (119.6 +/- 5.4 mg/dl vs 149.1 +/- 4.2; p less than 0.05) as well as insulin requirements (3.2 +/- 0.8 U vs 13.3 +/- 1.9; p less than 0.01) for the 180 min postprandial period. Similarly, glucagon level was reduced 30 min postprandially (24 +/- 6 pg/ml vs 59 +/- 24; p less than 0.05) and so GH level only 180 min after lunch (p less than 0.05). The premeal injection of SMS decreases postprandial glycemic excursions and the corresponding insulin requirement. The action of SMS 201-995 may be mainly mediated by the suppression of postprandial glucagon peak.