Distributions of components of benzene - ethanol, benzene - aniline and benzene - nitrobenzene mixtures between aqueous and gaseous phase were determined in dependence on the composition of the mixtures. Additivity of the distribution coefficients of the components was tested. The dependences of the distribution coefficients K on the molar ratios R of compounds in the mixtures were compared with that of the acute toxicity index EC50 (Tubifex tubifex). The most pronounced changes in the distribution coefficients were found for the benzene - ethanol mixture, the smallest for the benzene - nitrobenzene mixture. A deviation of K from the additive behaviour was demonstrated. Changes in total normalized concentration of components in the gaseous phase in the distribution coefficients correspond relatively well to changes in the EC50 index for the benzene - ethanol mixture. For the benzene - aniline mixture, the total normalized concentration of components in the gaseous phase was a good descriptor of the acute toxicity changes. The hypothetical possibility of using QSAR analysis for prediction of acute toxicity of binary mixtures of chemicals as a function of R and K has become more real.