This work was undertaken to investigate the effect of somatostatin on intestinal glucagonlike immunoreactivity (GLI) secretion in man. In normal subjects GLI release is slightly stimulated by oral glucose while this sugar evokes a much greater GLI response in gastrectomized patients. Therefore, our study was performed in a group of such patients (N=6). As expected, in the control experiments glucose ingestion elicited a clear-cut elevation of GLI plasma levels as measured with two antisera, 78J and R-8 (maximal peaks: 340% and 150% above basal values, respectively). Somatostatin infusion did not modify fasting GLI concentrations but completely abolished GLI response to glucose. Termination of the infusion was followed by a rebound of circulating GLI. The well-known suppressor effect of somatostatin on glucagon and insulin secretion was also detected. Finally, during somatostatin infusion the initial elevation of blood sugar after oral glucose, in the absence of insulin response, appeared considerably delayed. Our data demonstrate that somatostatin behaves as a potent inhibitory agent of GLI secretion in man. A retarding effect of somatostatin on glucose absorption is also compatible with our results.