A model for changes of electrical conductivity in the course of solid-state reaction has been demonstrated; it describes well the changes in the electrical conductivity of the reacting mixture ZnSe + Cr 2Se 3. The measurement method, the experimental data and the results calculated from the formulas derived in a previous publication have been presented. The experimental and theoretical curves of the temperature dependence of the electrical conductivity have similar shape. The theoretical values differ a little from the experimental ones. These differences allowed us to estimate the character of the changes of the concentration of defects in the product in the course of the reaction. Analysis of the assumptions and the application of the formulas previously presented was made.