During hemodialysis in a methanol poisoned patient, formate elimination followed first order kinetics with a plasma half-life of formate of 165 min. The mean dialysator (1.6 m2) clearance of formate was 148 ml/min (n = 8, SD +/- 11, range 128-161) at a blood flow of 215 ml/min. By applying first order kinetics, a volume of distribution of 0.5 l/kg was found, assuming that the dialysator clearance equals the total body clearance of formate. Formate, the main toxic agent in methanol poisoning, is thus probably more effectively removed by hemodialysis than methanol. This fact, and the very slow endogenous methanol elimination during appropriate ethanol treatment, should be considered when deciding on the treatment of a methanol poisoned patient presenting with metabolic acidosis.