This study compares the neuromuscular blocking effect of vecuronium (0.1 mg/kg) on the diaphragm and the adductor pollicis in nine anesthetized patients. Monitoring of the diaphragm consisted of measurement of the transdiaphragmatic pressure after bilateral phrenic nerve stimulation. Onset time for neuromuscular blockade of the diaphragm was 1.6 +/- 0.3 min (+/-SD) compared to 2.5 +/- 0.3 min in the adductor pollicis (P less than 0.001). The diaphragm recovered earlier and more rapidly than the adductor pollicis. The twitch height (TH) returned to 25% of its control value after 27 +/- 8 min for the diaphragm, compared to 41 +/- 11 min for the adductor pollicis (P less than 0.01). Complete TH recovery was achieved after 49 +/- 14 min for the diaphragm and after 74 +/- 22 min for the adductor pollicis (P less than 0.01). The recovery index of 12 +/- 4 min for the diaphragm was significantly shorter (P less than 0.05) than for the adductor pollicis (20 +/- 9 min.) We conclude that monitoring of peripheral muscles in anesthetized patients given vecuronium provides adequate information about the degree of paralysis of the diaphragm.