Edrophonium and neostigmine are anticholinesterase drugs used commonly to antagonize competitive neuromuscular block. Although it has a faster onset of action than neostigmine, edrophonium is unreliable when used to antagonize deep neuromuscular block. We have compared the antagonist characteristics of these two drugs when used to antagonize a moderate degree of pancuronium- or tubocurarine-induced neuromuscular block. Forty ASA I or II patients undergoing surgical procedures were allocated randomly to receive either pancuronium 70 micrograms kg-1 or tubocurarine 0.5 mg kg-1, and to receive either edrophonium 0.5 mg kg-1 or neostigmine 0.05 mg kg-1. Antagonism was attempted when the first response to train-of-four (TOF) stimulation recovered spontaneously to 25% of the control height. Neuromuscular function was monitored using the evoked integrated electromyogram of the first dorsal interosseous muscle of the hand. Adequate recovery was defined as the achievement of a TOF ratio of 0.70 or greater. Only seven of 20 patients who received edrophonium demonstrated adequate recovery 30 min after antagonism. Under the conditions described in this study, edrophonium 0.5 mg kg-1 was less effective as an antagonist than neostigmine 0.05 mg kg-1.