The present investigation was undertaken to ascertain whether the ketone body, beta-hydroxybutyrate (BOH), affects the somatostatin secretion from the isolated pancreas of normal and streptozotocin (STZ)-diabetic dogs. We found (1) that the addition of 10 mM DL-BOH to the perfusate augmented somatostatin secretion from the normal dog pancreas. The responses obtained were, however, modified by the prevailing glucose level with higher responses appearing at high (11 mM) rather than at zero glucose. The effect of BOH could not be attributed to changes in osmolarity, Na+, or H+ concentrations. (2) BOH at doses well within the physiologic and pathophysiologic range stimulated the secretion of somatostatin from the normal pancreas in a dose-dependent manner. The threshold concentration was close to 1 mM corresponding to 0.5 mM of the biologically active D form. (3) In the STZ-diabetic dogs, BOH (1-20 mM) elicits a dose-related enhancement of the pancreatic somatostatin secretion. In the two groups, identical D-cell responses were obtained at 3, 10, and 20 mM BOH. The results demonstrate that physiologic levels of BOH stimulates the release of somatostatin from pancreas of normal and STZ-diabetic dogs, thereby providing support for a physiologic influence of BOH over the secretory function of the pancreatic D-cell. The possible existence of a BOH-somatostatin feed-back mechanism operating in the diabetic organism is discussed.