BACKGROUND Xenotransplantation of porcine islets could be a valuable alternative to the shortage of human islets for transplantation. To overcome the immunological obstacle of antibody-mediated rejection, pigs homozygous for alpha1,3-galactosyltransferase gene knock-out (GT-KO) have been produced. The effect of this mutation on glucose metabolism is unknown. METHODS Glucose, insulin, C-peptide and glucagon levels were studied in eight adult pigs (four wild-type [WT] and four GT-KO) during intravenous glucose tolerance test (IVGTT), arginine stimulation test (AST), and insulin tolerance test (ITT). Morphological analysis of the pancreata was also performed. The in vitro insulin response to a high glucose concentration and theophylline were studied in a dynamic perfusion system with isolated islets. RESULTS Basal and stimulated blood glucose levels were similar in WT and GT-KO pigs. Basal insulin, C-peptide and glucagon were higher in GT-KO pigs. C-peptide and insulin responses to arginine and glucose were also higher in GT-KO animals. The reduction in blood glucose during ITT and IVGTT was similar in WT and GT-KO pigs. The extent of staining for insulin and glucagon in the pancreata were similar. The basal insulin secretion of isolated islets was higher in GT-KO pigs, while stimulation indexes for glucose and theophylline were similar to WT. CONCLUSIONS GT-KO pigs demonstrated differences in glucose metabolism compared to WT pigs, the cause for which remains uncertain. It is unlikely that these differences would in any way affect the outcome of GT-KO porcine islet xenotransplantation.