The effect of tofizopam on 3H-flunitrazepam binding was studied in rat hippocampus and cerebellum. Tofizopam (at a concentration of 10(-7) M) increased 3H-Flu binding through a 30% rise in the Bmax with no modification of Kd in either brain area. Similar results were obtained when the binding was measured in tofizopam (50 mg/kg p.o.) pretreated rats. Even though tofizopam has no anticonvulsive action against pentetrazol-induced convulsions, it significantly potentiated the action of diazepam but with no modification of brain diazepam levels and metabolism. The brain levels of tofizopam are reported and compared to plasma levels after oral administration of 5 and 50 mg/kg to rats.