1. Six female Caucasian patients received i.v. doses of propofol (2.7 +/- 0.3 (SE) mg/kg) for induction of anaesthesia. Anaesthesia was maintained with nitrous oxide, oxygen and enflurane for periods up to 3 h. A total urine collection was made from each subject for 24 h after administration of propofol; samples were concentrated and analysed for propofol metabolites by nmr spectroscopy. 2. By 24 h, 50.9 +/- 4.0% of the dose of propofol was recovered as metabolites. The proportions of propofol metabolites, 1-quinol glucuronide (1-QG), 4-quinol glucuronide (4-QG), propofol glucuronide (PG) and 4-quinol sulphate (4-QS) recovered in urine (0-24 h) of the patients were 12 +/- 1, 8 +/- 2, 76 +/- 4 and 4 +/- 1% respectively. However, one patient showed a metabolite profile in which PG comprised 93% and 1-QG 7% of the total metabolites. 3. Nmr spectroscopy has been shown to be a satisfactory method for the quantification of propofol metabolites in urine without the necessity for reference samples.