The solubility of the biologically active substances, salinazid and vanillin isoniazid, was measured in the buffer solutions (pH 2.0 and 7.4) and in octanol within the temperature range from (293.15 to 313.15) K. The solubility of the compounds in all the investigated solvents was revealed to be less than 10(-3) mole fraction and increases with the solvents in the order: buffer at pH 7.4 < buffer at pH 2.0 < octanol. The enthalpies of dissolution and solvation were calculated. The temperature dependences of the distribution coefficients in the system buffer at pH 7.4/octanol system were obtained and the transfer thermodynamic functions were derived. The distribution coefficients were used to predict the solubility of the studied compounds in aqueous medium.