A role of gamma-amino butyric acid (GABA) in benzodiazepine actions is supported by the GABA stimulation of membrane-bound and soluble benzodiazepine receptors and preliminary evidence that GABA protects benzodiazepine receptors from heat inactivation. We show here that the GABA receptors labelled by by 3H-muscimol possess a benzodiazepine recognition site, as benzodiazepines, in proportion to their pharmacological activity, protect 3H-muscimol binding from inactivation by heat and the protein modifying reagent iodoacetamide. We also show that benzodiazepines and GABA act at apparently distinct sites to protect benzodiazepine receptors from heat and iodoacetamide.