The effect of an iv infusion of somatostatin (SRIH) (4.1 micrograms/min x 90 min) on the basal secretion of arginine-vasopressin (AVP) and on the AVP response to insulin (0.15 IU/Kg) - induced hypoglycemia was studied in 6 normal men. Basal AVP secretion was not modified by SRIH administration. The blood glucose decrements induced by insulin were similar in the control insulin-tolerance test (ITT) and in the ITT + SRIH test, whereas the AVP response to hypoglycemia was significantly lower in the presence of SRIH. The mean peak AVP increase was three times higher than the basal value in the control ITT, but only two times during SRIH administration. Infusion of higher doses of SRIH (7 micrograms/min x 90 min) produced similar results. These data suggest the involvement of a somatostatinergic mechanism in regulation of AVP response to hypoglycemia.