Plasma and urine concentrations of d-tubocurarine (d-TC) were determined and twitch tension was monitored before and after the intravenous administration of d-TC, 0.5 mg/kg in patients anethetized with halothane and nitrous oxide with (N=5) and without (N=5) renal failure. Terminal half lives of d-TC of 231 and 330 minutes predicted from other studies for patients with and without renal function were consistent with plasma concentrations measured. In patients with normal renal function, 38% of unchanged d-TC was eliminated in urine in 25 hours as opposed to 13% in those patients with a newly transplanted kidney. However, we still conclude that a newly transplanted kidney can eliminate d-TC effectively since the kidney was inserted 3.5 hours after administration of d-TC. Absence of renal function significantly prolonged the duration of neuromuscular blockade but did not alter the plasma concentrations of d-TC required for neuromuscular blockade. Thus, prolonged neuromuscular blockade from d-TC in patients with renal failure is due to decreased elimination rate of the drug as a consequence of lack of renal function rather than increased sensitivity.