Lipophilicity plays a significant role as a determinant of biological properties. Reversed-phase high-performance thin layer chromatography (HP-TLC) was applied to determine the log P values of chelidonine, allocryptopine, sanguinarine chloride and chelerythrine chloride at three different pH values: 3.0, 7.4 and 10.0. The mobile phase was a mixture of acetonitrile and water with different concentrations of acetonitrile (50-75 vol%). The retention factors, R-m0 values, for the compounds with known log P and for the analyzed substances were determined. The log P values obtained experimentally were compared with the theoretical data obtained by using known algorithms (miLogP, xLogP, and AlogPs). Additionally, log D values of the examined substances were determined. The highest log P value was observed for chelerythrine chloride in an alkaline environment, while the lowest one was noted for chelidonine at acidic pH.