  We derive the exact solution of the Boltzmann kinetic equation for the
three-dimensional Lorentz model in the presence of a constant and uniform
magnetic field. The velocity distribution of the electrons reduces
exponentially fast to its spherically symmetric component. In the long time
hydrodynamic limit there remains only the diffusion process governed by an
anisotropic diffusion tensor. The systematic way of building the Chapman-Enskog
solutions is described.
