The gastrointestinal absorption of zinc by haemodialysis patients has been investigated. Subnormal plasma zinc responses were observed in nine haemodialysis patients during oral zinc tolerance tests. These patients also had reduced leucocyte zinc concentrations which did not respond when 50 mg (0.77 mmol) of zinc was given daily by mouth for a period of 4 months. White cell zinc concentrations measured in another group of 10 haemodialysis patients were reduced initially, but rose to normal levels over 4 months when zinc was added to the fluid used for dialysis. These data suggest that the intestinal absorption of zinc was defective in the dialysis patients participating in this investigation.