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BACKGROUND: Acceleromyography (AMG) is being employed with increasing frequency as a research tool. However, there is almost no information available regarding the accuracy of values for drug potency obtained using AMG. This study was an attempt to determine if AMG-derived ED(50/95) values are interchangeable with those measured with a more traditional neuromuscular monitor. METHODS: Thirty adult patients were studied. Anesthesia was induced and maintained with N20, propofol, and supplementation opioid. Tracheal intubation was accomplished without muscle relaxants. Simultaneous ipsilateral AMG and EMG responses to 0.10 Hz stimulation was recorded. Following instrument calibrations, a single dose of rocuronium was administered. The first patient received a bolus of 0.17 mg kg(-1) of rocuronium. Using the Hill equation with a postulated slope of 4.50, the ED(50) was calculated. The second subject received a dose which approximated the calculated ED(50) for patient no. 1. Successive subjects were given a dose based on the running average of the estimated ED(50). RESULTS: The AMG-derived ED50/95 values for rocuronium (0.163 +/- 0.055 and 0.314 +/- 0.105 mg mg(-1)) were virtually identical to those established using EMG (0.159 +/- 0.043 and 0.306 +/- 0.084 mg kg(-1)). While mean peak twitch depression (Delta T1) was the same in both groups for individual subjects Delta T1 differed by +/- 20% (95% confidence interval). DISCUSSION: Acceleromyography-derived twitch heights for individual patients are not necessarily interchangeable with information obtained using electromyography. Nevertheless, acceleromyography appears to be a valid methodology for determining the drug potency when a population rather than an individual subject is being studied