The effects of age on the pharmacokinetics and pharmacodynamics of vecuronium in eight elderly patients aged 72-86 yr and eight younger adults aged 26-48 yr undergoing elective surgical procedures under nitrous oxide-fentanyl anesthesia were studied. Vecuronium (0.1 mg/kg) was given as an intravenous bolus, and the ulnar nerve was stimulated with a square-wave impulse of 0.2-ms duration. The response to stimulation at a frequency of 0.1 Hz was measured and recorded with a force displacement transducer applied to the thumb. Spontaneous recovery was significantly longer in elderly patients than in younger patients (50% recovery time, 97.1 +/- 29 vs 39.8 +/- 14 min, mean +/- SD; recovery index [25%-75%], 49.4 +/- 11 vs 15.0 +/- 8 min). In addition, in elderly patients elimination half-life of vecuronium was significantly prolonged (125 +/- 55 vs 78 +/- 21 min, P = 0.04) and plasma clearance reduced (2.6 +/- 0.6 vs 5.6 +/- 3.2 mL.kg-1.min-1, P = 0.049). The prolonged duration of action of vecuronium in the elderly surgical patients thus appears to be secondary to altered pharmacokinetics consistent with an age-related decrease in renal and hepatic functions.