We determined the dose-response relationship, the onset time, the duration, and the recovery time of a rocuronium neuromuscular block under four anesthesia techniques. Patients were equally randomized to four different groups (n = 20) receiving 0.5%-1% halothane, 1.5%-2% enflurane, 1.2%-1.8% isoflurane end-tidal concentration in 34%/66% O2/N2O, or 6.0 mg.kg-1 x h-1 propofol without N2O for anesthesia and alfentanil for analgesia. Strength of thumb adduction in response to single and train-of-four stimulation of the ulnar nerve was quantitated. Rocuronium 0.15, 0.2, 0.25, and 0.3 mg/kg were given intravenously. When maximal depression of twitch tension occurred, supplemental doses up to a total of 0.5 mg/kg were given. If required, additional doses of 0.15 mg/kg were given at 25% recovery of control twitch tension. Standard hemodynamics, end-tidal CO2, and anesthetic gas concentrations were monitored continuously. The mean ED50 (SD) was 0.133 (+/- 0.009) mg/kg for the halothane group, 0.118 (+/- 0.012) mg/kg for the enflurane group, 0.069 (+/- 0.026) mg/kg for the isoflurane group, and 0.167 (+/- 0.007) mg/kg for the total intravenous anesthesia (TIVA) group, respectively. There was a statistically significant difference between the halothane and TIVA, and between the enflurane and TIVA groups (P < 0.05). Rocuronium has a short onset time and an intermediate duration of action. The neuromuscular blocking potency and pharmacodynamic profile are moderately influenced by volatile anesthetics.