Fifty patients anaesthetized with nitrous oxide-oxygen, supplemented by thiopentone and pethidine, thiopentone and halothane, or droperidol and fentanyl, who received tubocurarine for the maintenance of muscular relaxation were divided into five groups each of ten. At the end of anaesthesia, the patients of groups A and B received intravenously atropine 6 /ig/kg and neostigmine 20 yug/kg, those in groups C and D atropine 12 /fg/kg and neostigmine 40 /ig/kg, and those in group E atropine 8 /ig/kg and neostigmine 20 /ig/kg. In groups A and C atropine was injected in 60 seconds and was followed 1 minute later by neostigmine also administered in 60 seconds. In groups B, D, and E atropine and neostigmine were injected together in 60 seconds. Reversal of residual neuromuscular block was achieved in all five groups without the development of any serious arrhythmias. Statistically significant tachycardia developed only in those groups (A and C) in which atropine was injected 2 minutes before the administration of neostigmine. Of the different dosages and sequences of administration investigated, the combined injection of atropine 6 /tg/kg and neostigmine 20 /tg/kg over 60 seconds appears to be most suitable for the reversal of residual neuromuscular block.