The antileptazol effect of CP 1414 S (7-nitro-2-amino-3-phenyl-3H-1,5-benzodiazepine-4-one) a newly developed 1,5 benzodiazepine, lasts longer in mice than in rats. After intraperitoneal injection (10 mg/kg) brain levels of the drug were higher and persisted for longer in the mouse than in the rat. Although it cannot be excluded tht possible metabolites of CP 1414 S may contribute to the anticonvulsant effect of CP 1414 S, in both species the protective effect correlates well with the brain concentrations of the drug.