The general method for the development of finite difference equations for heterogeneous reactors is presented. These equations are similar to those used in the usual homogenization method although a new expression for calculating the coefficients makes these equations more precise. It is shown that, together with average absorption, multiplication, and group-to-group transition cross sections for cells without neutron exchange, it is necessary to use similar values for cells with unit neutron current at the cell boundaries for some groups. It is also necessary to use the cell tilt factors for neutron fluxes.