In this study, the thin layer chromatographic behaviour of some acidic and neutral drugs and the reproducibility of HRf values obtained were investigated. In addition when urin was selected as a biological material, the influence of the biological matrix on the results of chromatographic analysis was also investigated after solvent extraction of drug substances from spiked urine samples. Chromatographic studies were performed on the plates prepared in laboratory and obtained commercially too, by using chloroformacetone (4:1) solvent system. Keywords :