To compare the time course of neostigmine and edrophonium antagonism of varying intensity neuromuscular blockade induced by atracurium, pancuronium, or vecuronium, the authors studied 98 patients anesthetized with nitrous oxide (60%) and halothane or enflurane. Neuromuscular blockade, as monitored by single stimulusinduced twitch tension (TT), was antagonized at varying degrees of spontaneous recovery (2–80% of control TT). Time to antagonism (time from injection of neostigmine or edrophonium to 90% recovery of control TT) was not different between edrophonium, 0.5 mg/kg, and neostigmine, 0.04 mg/kg, when spontaneous recovery had been allowed to occur to at least 11 % of control TT prior to antagonist administration (P> 0.05). For profound neuromuscular blockade (TT ≤ 10% of control) induced by pancuronium or vecuronium, time (mean ± SD) to antagonism with neostigmine, 0.04 mg/kg, was 7.0 ± 2.2 min and 5.6 ± 1.7 min, respectively, while the same for edrophonium, 0.5 mg/kg, was 20.0 ± 8.0 min and 15.0 ± 12.5 min, respectively (P< 0.05). Time to antagonism of profound atracuriuminduced neuromuscular blockade was 8.5 ± 3.3 min for neostigmine, 0.04 mg/kg, and 9.8 ± 7.0 min for edrophonium, 0.5 mg/kg, (P> 0.05). For profound vecuronium- and pancuronium-induced neuromuscular blockade, time to antagonism by edrophonium, 1.0 mg/ kg, was 4.6 ± 3.0 min and 3.9 ± 1.6 min respectively. The authors conclude that neostigmine, 0.04 mg/kg, antagonizes neuromuscular blockade within 12 min when TT is greater than 2% of control at time of reversal. When TT is greater than 10% of control, edrophonium, 0.5 mg/kg, produces similar time to antagonism. However, when TT is 2–10% of control, the dose of edrophonium dose should be at least 1.0 mg/kg to be as rapid as neostigmine, 0.04 mg/kg.