The aim of the study was to investigate the offset time of atracurium when given by continuous infusion on a paediatric intensive care unit and to look for evidence of tolerance. Over a period of 8 months, 20 mechanically ventilated children had a steady-state infusion of atracurium discontinued to enable the assessment of their level of sedation. The offset time of atracurium was assessed by train-of-four (TOF) stimulation of the ulnar nerve. The initial TOF reading was documented as was the time taken to reach a TOF ratio of 0.9. Thirty-five assessments were carried out. The mean offset time of atracurium was 28.7 min (SEM 1.76 min, range 8-56 min). There was no correlation between the dose of atracurium at discontinuation and the offset time of the infusion. The duration of infusion was negatively correlated with the offset time of atracurium, and this effect was most prominent in children who had received infusions for longer than 48 h. When given by continuous infusion, the offset time of atracurium is very variable between individual patients. Infusions administered for longer than 48 h are associated with a significant reduction in the offset time as a result of increasing tolerance.