An investigation has been made of the behaviour of fast electrons in toroidal discharges. The kinetic equation, describing the evolution of the fast particle distribution has been derived and analysed. A semi-analytical solution of the kinetic equation has been obtained in the superthermal energy region. The external electric field, turbulence, the non-uniformity of the mean magnetic field and collisions are shown to be important factors affecting the distribution function. The role of the ambipolar electric field has been established and identified as an essential factor in the process of fast electron diffusion. The strong influence of the density profile on the diffusion of fast particles is clearly demonstrated. A comparison has been made with experimental data obtained on the ZT-40M device. Agreement with the results of these experiments is observed