The duration of action and the pharmacokinetics of vecuronium were compared in patients with and without renal function. Twenty patients were studied: 12 with renal failure who were to receive kidney transplants from cadaveric donors, and eight with normal renal function. After oral premedication with diazepam, 10 mg, anesthesia was induced with thiopental, 4 mg/kg iv, and maintained with the inhalation of 60% nitrous oxide and 0.9-1.1% isoflurane, end-tidal concentration, in 40% oxygen. The force of thumb adduction in response to supramaximal ulnar nerve stimulation was monitored and recorded. An intravenous bolus of vecuronium, 0.1 mg/kg, was administered after 15 min of a stable end-tidal isoflurane concentration, as measured by mass spectrometry. Venous blood was then sampled at frequent intervals for 4 h following the bolus. Vecuronium concentrations in plasma were quantified by a sensitive and specific gas chromatographic assay. Data were analyzed by nonlinear least squares regression and described by a two-compartment model. The duration of neuromuscular blockade was longer in patients with renal failure than in those with normal renal function. This increased duration may be related to both a decreased plasma clearance and a prolonged elimination half-life of vecuronium in the renal failure group.