Elevated serum levels of gastrin, pancreatic polypeptide, and glucagon were found in 10 uraemic patients, whereas gastric inhibitory polypeptide and somatostatin levels were normal. After renal transplantation there was a significant reduction in serum gastrin (median, 5 pmol/l; p = 0.05, n = 9), pancreatic polypeptide (145 pmol/l; p less than 0.01, n = 9), GIP (9.5 pmol/l; p = 0.02, n = 7), and glucagon (92 pg/l; p less than 0.02, n = 9), whereas no alteration was seen in the somatostatin level. Meal stimulation produced consistent increases in serum levels of all hormones, and the response appeared to be unchanged after renal transplantation.