Described is a thin-layer chromatography method for the demonstration and identification of the cumarin derivatives cumaphos and warfarin. Tested were five solvents and six developers. Best results were obtained by means of Silica gel plates, the toluol-aceton solvent (85:15), and the developer of a diazosalt 0.4% in an alcohol 20% sodiumhydroxide. Warfarin and cumaphos are demonstrated with the appearance of yellow, resp. orange spots on a white background, the RF values being 0.37 and 0.85, and sensitivity as regards warfarin 0.5 microgram and cumaphos 0.2 microgram.