Intracerebroventricular injection of 1-kynurenine sulfate (10 micrograms) eliminated anticaffeine effect of diazepam (5, 10 and 20 mg/kg) in mice. Antipentylenetetrazole (0.5-2.5 mg/kg) and anticonflict (1-2.5 mg/kg) effects of diazepam were not altered by kynurenine (0.1-10 micrograms). The sedative effect of diazepam (1 and 4 mg/kg) was potentiated by kynurenine (1 microgram). Stimulation of locomotion induced by kynurenine (0.5 and 2.5 micrograms) was prevented or perversed by pretreatment with diazepam (1 mg/kg). In a conflict situation test, diazepam and kynurenine had an opposite action, respectively increasing and decreasing the number of transitions between light and dark compartments. The central effects of kynurenine can be related and not related to benzodiazepine receptors.