The pharmacokinetics of chlordemethyldiazepam--a pharmacologically very active new 1,4-benzodiazepine derivative--in healthy subjects after administration of a single oral dose of 2 mg, was studied. Peak concentrations were reached in 1.2 +/- 0.2 hours. Plasma levels declined with a biphasic pattern, and the elimination phase had a half-life of 82.9 +/- 14.1 hours. The concentrations of the main metabolite of chlordemethyldiazepam, lorazepam, were about 7% of those of the parent compound. In urine only conjugated lorazepam could be found its 96 hour excretion reaching about 15% of the administered dose of parent drug.