Some new derivatives of thiosemicarbazide and the 1,2,4-triazole of sulphanylacetic acid have been chromatographed on RP-18 HPTLC plates with mobile phases containing water and an organic modifier (methanol, dioxane, acetone, 2-propanol, or tetrahydrofuran). Relationships between solute retention and modifier concentration were described by Snyder's linear equation. The equation was used to determine RM0 values, by extrapolation, and the S values denoting the slopes of the relationship between linear retention and mobile phase concentration; both values characterize the lipophilicity of the substances. Calculated values of RM0 were correlated with log P values for the drugs investigated by use of the software HyperChem. Correlations between intercept (RM0) and slope (S) from the linear equations were also calculated. The effects of different mobile phase modifiers on experimentally obtained lipophilicity were also analysed and compared.