In order to study the mechanism or insulin release ny xyiitoi ana glucose, in vitro experiments were done in dog pancreas tissue, using the method described by Malaisse et al. Xylitol and glucose in low concentration (60mg/100ml) did not stimulate insulin release above base line values observed in the absence of sugar. High concentration of xylitol and glucose (300mg/100ml) stimulated insulin release significantly, but the amount of insulin released by xylitol was not so much as that by the same concentration of glucose. The insulin-stimulatory effects of glucose and xylitol were inhibited by the addition of epinephrine or propranolol. 2, 4-dinitrophenol blocked them, too. Mannoheptulose inhibited the release of insulin by glucose, but it had no significant effects on xylitol-induced insulin release. These results suggest that xylitol has a direct insulinstimulatory effect in dog pancreas tissue and that there may be a common path in the mechanism of insulin release by xylitol and glucose after it has been metabolized in pancreatic islets.