In chronic renal failure both Hb A1 and Hb Aιc levels have been reported to be elevated. In order to investigate the causes of such increase we measured Hb A1 (cation-exchange chromatography), blood urea nitrogen, arterial blood pH and plasma bicarbonate in 40 patients with chronic renal failure receiving conservative treatment, 45 uremic patients on intermittent hemodialysis and 60 subjects with normal renal function. In patients with chronic renal failure Hb A1 highly correlates with arterial blood pH and plasma bicarbonate, thus emphasizing the major role played by uremic acidosis in the increased Hb Ai fraction in chronic renal failure