A highly sensitive, quantitative assay procedure for ketamine and two of its metabolites, based upon gas–liquid chromatography of a heptafluorobutyryl derivative, has been developed. No appreciable interference occurred with procaine, atropine, meperidine or promethazine. Anesthetic doses in man (iv) produced ketamine plasma levels above 1 μg/ml, with a biological half-life of 17 min. The presence of the N-dealkylated metabolite of ketamine in human plasma was clearly demonstrated.