Background/Aims: Human body fluids such as serum, cerebrospinal fluid and saliva contain a variety of proteins. Since kynurenic acid (KYNA) has been detected in human saliva, we wondered whether KYNA could be produced in cat saliva by KYNA-synthesising enzymes, namely kynurenine aminotransferases KAT I, KAT II and KAT III. Methods: Saliva was collected from domestic cats. KAT activity was measured by enzymatic method and KYNA produced was determined by high performance liquid chromatography. Results: Cat saliva is capable of producing KYNA by the action of KAT I, KAT II and KAT III. KAT activities were measured between 500 and 2500 fmol/ µl saliva/h. Interestingly, diluted cat saliva showed a significantly higher capacity to synthesise KYNA, suggesting the presence of endogenous inhibitors. This effect was particularly evident for KAT III and KAT II and to a lesser extent for KAT I. Cat saliva contains KYNA in the nM range. Conclusion: Our data demonstrated for the first time the presence of KAT I, KAT II and KAT III proteins in cat saliva. Furthermore, our data suggest the presence of compounds/factors in cat saliva that may be involved in the modulation of the biochemical machinery of the kynurenine pathway, such as the synthesis of KYNA. The endogenous modulation of KYNA formation in the feline mouth may play a pivotal role in various physiological and pathological events.