Plasma concentrations of pancuronium following single dose administration in six patients, and following multiple dose administration in four patients, all undergoing renal transplantation surgery, were measured using a fluorimetric method. A two-compartment open model was used in the pharmacokinetic analysis of the data. Comparison of the pharmacokinetic findings with data previously obtained for patients undergoing elective surgery but having normal renal function indicated that the clearance of the drug was reduced significantly in the patients with renal failure, and that in these individuals the half-life was increased significantly. Measurement of the evoked mechanical twitch response concurrently with plasma concentration monitoring of pancuronium confirmed that the prolongation of half-life in the patients with renal failure was often but not always associated with an extended duration of neuromuscular blockade and furthermore that the rate of recovery from block might also be prolonged. The clinical implications of these findings are discussed.