Train-of-four (TOF) responses were assessed in 70 patients (seven groups of ten patients each) during recovery of neuromuscular block from atracurium (226 or 452 micrograms/kg), vecuronium (40 or 80 micrograms/kg), pancuronium (60 or 120 micrograms/kg) and tubocurarine (450 micrograms/kg) in order to quantify the height of T1 (first response in the TOF sequence) at which T2, T3 and T4 (2nd, 3rd and 4th response in TOF sequence) reappear. Patients were anaesthetised with thiopentone, nitrous oxide in oxygen and fentanyl. There were small but significant differences between relaxants. The clinically useful parameter, i.e. the 4th response in the TOF sequence, appeared at approximately 30% height of the first response (T1) rather than at 25% as generally believed. It is suggested that the third response in the TOF sequence, which reappeared at an average height of T1 of about 25% be used for administration of further supplements of muscle relaxants since abdominal muscle relaxation becomes inadequate at this stage.