[en] A generalized hydrodynamical equation system was constructed in which the anisotropy of the momentum distribution is added as a new variable. These equations are derived from the moment equations of the relativistic Boltzmann equation where the closure of the set is achieved by assuming a particular class of initial conditions. The equations are then explicitly solved for two uniform interpenetrating hadron streams. The collision cross-sections are the bare hadron cross-sections; the presence of the other hadrons can be simulated by the use of a density and energy density dependent temperature and mass, taken from self-consistent calculations. The results are compared with other theoretical results. It was found that the isotropization occurs sufficiently rapidly for medium energy head-on collisions to reach local thermal equilibrium. (author)