In a dark-light chamber in mice, kynurenic acid (KYNA, 200 mg/kg, i.p.), an endogenous neuroactive metabolite of tryptophan, attenuated the most stable effect of anxiogens in this model of anxiety--a decrease in the rate of leanings-out of the dark compartment --induced by caffeine, pentylenetetrazole and yohimbine, but not by beta-phenylethylamine (PEA). KYNA by itself did not alter behavior of mice in the chamber, in contrast to what has been observed in an elevated plus-maze, another model of anxiety, where KYNA had an anxiolytic pharmacological profile.