The effects of FK506 on exocrine function of the pancreas in Sprague-Dawley rats were examined and compared with those of cyclosporine. FK506 did not affect the levels of amylase and lipase in the pancreas of rats given the drug orally in a daily dose of 1 or 5 mg/kg for 2 weeks. Furthermore, the pancreas of the rats showed good exocrine secretion of enzymes such as amylase and lipase on stimulation with carbachol in vitro. Cyclosporine 50 mg/kg given in the same way as FK506 also was free of effect on enzyme levels in the rat pancreas, but the exocrine secretion of the enzyme from the pancreatic lobules on stimulation with carbachol was impaired. It is concluded that FK506 does not affect pancreatic exocrine function in rats.