Similarly to clozapine, a clozapine metabolite, N-desmethylclozapine, but not clozapine N-oxide, antagonized brain γ-aminobutyric acid type A (GABA(A)) receptors at high micromolar concentrations. However, daily subcutaneous injections of clozapine (10 and 25 mg/kg) and haloperidol (0.5 mg/kg) for 14 days failed to alter the modulation by GABA of rat cerebrocortical and cerebellar benzodiazepine ([H]flunitrazepam) or convulsant (t-[S]bicyclophosphorothionate) binding sites of the GABA(A) receptor. The results thus suggest that the GABA(A) receptor antagonism exerted by chronic in vivo clozapine treatment is weak as compared to this treatment's actions on certain monoamine receptors and is unlikely to be involved in the therapeutic actions of clozapine.