A case of a patient with tetanus is reported in whom an atracurium infusion and artificial ventilation were needed in addition to sedation to control the muscle spasms. The atracurium infusion was used for 71 days, the longest time ever recorded, at a mean rate of 1.3 mg/kg/hour at the end of infusion. The plasma atracurium and laudanosine concentrations were 1.5 micrograms/ml and 0.985 micrograms/ml respectively. Subsequently there was an exponential decline in the serum laudanosine concentration which had decreased to 0.014 micrograms/ml 24 hours later. These results suggest that prolonged use of atracurium by infusion is not associated with excessive cumulation of laudanosine when renal and hepatic function are normal.