The effects of tryptophan (Trp) metabolites administered into right cerebroventricle (1μmol) on the electrocorticograms (ECoG) of rats were studied to investigate the roles of Trp metabolites in the brain function. Kynurenine, anthranilic acid, and xanthurenic acid has no effect on ECoG until the end of recording 4 hours after the administration. 3-Hydroxykynurenine had a suppressive effect on the ECoG transitory, and kynurenic acid suppressed ECoG slightly. 3-Hydroxyanthranilic acid which is a metabolite of 3-hydroxykynurenine, induced spike discharges with a long latency (60-230 min after the administration). 3-Hydroxyanthranilic acid is thought to be metabolized to o-aminophenol, quinolinic acid and picolinic acid. Among the 3-hydroxyanthranilic acid metabolites, o-aminophenol induced spike discharges a few min after the administration, and the spike discharges a few min after the administrations, and the spike discharges lasted 60 min. On the other hand, quinolinic acid suppressed ECoG, and picolinic acid had no effect. These electrocorticographic findings suggest that 3- hydroxyanthranilc acid might induce spike discharges after metabolization to o-aminophenol.