A rapid method for evaluation of the functional activity of the monooxygenase system of the liver has been developed based on the thin layer chromatography (TLC) determination of the antipyrtine content in the saliva. Advantages of the proposed TLC method are the simplicity of sample preparation for the analysis, economy, rapid processing, and reliability. The method can be used to assess the detoxicating function of liver under clinical and outpatient setting conditions.