Plasma pyridoxal-5'-phosphate (PL-5'-P), pyridoxal (PL), pyridoxine (PN), and 4-pyridoxic acid (4-PA) were measured by high-performance liquid chromatography (HPLC) in 39 patients (15 male, 24 female) with chronic fenal failure undergoing regular haemodialysis and 46 healthy controls (28 male, 18 female). All three vitamers of vitamin B6 and the metabolite were significantly elevated in the haemodialysis patients. Mean PL-5'-P and PN concentrations were 20 times the mean in controls. Only one patient took a vitamin B6 supplement. In view of the neurotoxicity of supranutritional intakes of PN in normal humans we suggest that supplements of PN be carefully monitored when administered to patients with chronic renal failure.