Fasting levels of 5 gut hormones were studied in 30 patients with advanced uraemia (CRF), 40 undergoing regular dialysis (RD) and 555 renal transplant patients (RT). Mean values of gastrin and total glucagon were markedly elevated in CRF and RD patients compared with 20 normal subjects; there were lesser elevations in pancreatic glucagon, insulin and vasoactive intestinal peptide (VIP). Secretin levels were unchanged. In RT patients, fasting levels of VIP and pancreatic glucagon had returned to normal, while levels of gastrin, total glucagon and insulin remained slightly elevated compared with controls. Food stimulated hormone levels were measured in 18 RD patients and compared with 18 controls. After eating, RD patients failed to show the late increase in total glucagon, or the suppression of VIP and secretin seen in normal subjects; the pattern of gastrin and insulin response was similar to controls, but after the initial increase plasma levels in RD patients tended to show a slower decline. Thus involvement of the gastrointestinal tract in uraemia is associated with functional disturbance of the endocrine system of the gut.