The kinetic theory of microscopic particles moving in a dispersive and absorptive medium is constructed on the supposition that along a random path the radius vector of the particle, the unit vector along its velocity and its energy taken together form a Markov stochastic process. The processes of scattering in a homogeneous and isotropic medium are considered in detail when there are no energy changes. A solution to the kinetic equation is found for these processes for the case of an instantaneous point source of particles.