The influence of renal failure and of hepatic cirrhosis on the plasma protein binding of etomidate, an intravenous anaesthetic agent of basic nature, has been investigated. The percentage of free etomidate in plasma containing 1 &mgr;g/ml was markedly increased in patients with renal failure and in patients with hepatic cirrhosis, when compared with a group of healthy volunteers (43.4 ± 2.9% and 44.2 ± 2.1 versus 24.9 ± 1.4%). This decrease in binding correlated inversely with serum albumin levels in both conditions (r = -0.88 and r = -0.72, respectively) but a slight decrease in the amount bound per mole of albumin was also apparent in both types of disease.