The effect of a treatment with L-triiodothyronine (T3) or propylthiouracil (PTU) on the characteristics of benzodiazepine and chloride ion channel binding sites in rat hippocampus and cerebral cortex was studied using a radiolabelled technique. In our experimental conditions, neither hyper- nor hypothyroidism modified number and affinity of [3H]flunitrazepam or [3H]butylbicycloorthobenzoate (TBOB) binding sites. These data indicate that neither benzodiazepine nor chloride ionophore sites of the GABA complex are modified in an experimental condition of dysthyroidism.