Signs of neuromuscular block were evident more than 20 hours after the administration of alcuronium to an anuric patient. Complete recovery occurred during haemodialysis. We therefore decided to study the dialysance of three radioactive non-depolarising relaxants during haemodialysis of four patients with chronic renal failure. Although dimethyl tubocurarine and alcuronium were equal as regards dialysance, the concentration of the former, in plasma, falls faster than does alcuronium. It is believed that a larger volume of distribution occurs with dimethyl tubocurarine. In spite of the fact that the dialysance of muscle relaxants is small, haemodialysis might lower the concentration of these substances in the plasma to a level below the critical point which produces paralysis.