ISLET transplantation from rodents is a useful model for developing potential approaches to both xenografts and allografts in humans. One of the major obstacles to pancreatic islet transplantation is the limited yield of islets from the donor pancreas. It is difficult to obtain a sufficient number of islets from one donor to reverse hyperglycemia in one recipient. Furthermore, a high rate of primary nonfunction (PNF) and early graft failure is observed in xenogeneic islet transplantation, making it difficult to test new immunosuppressor drugs. Some studies have demonstrated that nicotinamide (NA), an inhibitor of poly-ADPribose synthetase, might have protective effects on islet isografts and allografts. NA administration has been shown to produce a low rate of PNF, with fast normalization of glycemia and with a low number of transplanted islets. NA might have protective effects on other tissues. The purpose of this study was to analyze the effects of NA in a concordant model of islet xenotransplantation in relation to the graft survival, the rate of PNF, and the time for glycemia normalization.