A sensitive method, using gas chromatography with nitrogen selective detection, has been developed for the accurate measurement of methohexitone, in plasma, in concentrations of less than 0.05 mug/ml, and which makes it possible to study the pharmacokinetics of the drug after clinical doses in man. Methohexitone sodium 3.0 mg/kg was administered by zero-order infusion to healthy volunteers and plasma concentrations were measured during and after infusion. The decrease in the plasma concentration of methohexitone can be described by two-compartment kinetics. The terminal elimination half-life of the drug is relatively short (70-125 min), which is a result of a high metabolic clearance rate (657-999 ml plasma/min). It was concluded that uptake of the drug by adipose tissue does not contribute significantly to its pharmacokinetics in man. In addition to the initial redistribution of an anaesthetic dose of methohexitone, the quick recovery of patients is a result of rapid metabolism of the drug.