Purpose: To examine the influence of continuing administration of sevoflurane or isoflurane during reversal of rocuronium induced neuromuscular block with neostigmine.Methods: One hundred and twenty patients, divided into three equal groups, were randomly allocated to maintenance of anesthesia with sevoflurane, isoflurane or propofol. Neuromuscular block was induced with rocuronium and monitored using train-of-four (TOF) stimulation of the ulnar nerve and recording the force of contraction of the adductor pollicis muscle. Neostigmine was administered when the first response in TOF had recovered to 25%. At this time the volatile agent administration was stopped or propofol dosage reduced in half the patients in each group (n = 20 in each group). The times to attain TOF ratio of 0.8, and the number of patients attaining this end point within 15 min were recorded.Results: The times (mean ± SD) to recovery of the TOF ratio to 0.8 were 12.0 ± 5.5 and 6.8 ± 2.3 min in the sevoflurane continued and sevoflurane stopped groups, 9.0 ± 8.3 and 5.5 ± 3.0 min in the isoflurane continued and isoflurane stopped groups, and 5.2 ± 2.8 and 4.7 ±1.5 min in the propofol continued and propofol stopped groups (P < 0.5-01). Only 9 and 15 patients in the sevoflurane and isoflurane continued groups respectively had attained a TOF ratio of 0.8 within 15 min (P < 0.001 for sevoflurane).Conclusions: The continued administration of sevoflurane, and to a smaller extent isoflurane, results in delay in attaining adequate antagonism of rocuronium induced neuromuscular block. REVIOUS studies have shown that antagonism of block with relaxants such as vecuronium is impeded in the presence of potent volatile agents such as sevoflurane and isoflurane. [1][2][3] It has also been shown that sevoflurane anesthesia potentiates the effect of rocuronium compared with isoflurane and propofol anesthesia. 4 Although there are reports of antagonism of rocuronium block with neostigmine, these have generally examined the influence of the dosage or the timing of administration of the anticholinesterase. [5][6][7] The aim of the present study was to examine the effect of the sevoflurane on the antagonism of rocuronium by neostigmine, and compare it with the effects of isoflurane, and intravenous anesthesia.