Free radical generation during the thermal decomposition of azoisobutyronitrile (AIBN) in nematic 5CB : 50CB mixtures has been studied by electron paramagnetic resonance (EPR) at 308-343 K. The kinetic model of primary radical cage escape in nematic mesophases is considered from the point of view of rotational and translational evolution of primary radical pairs ordered by anisotropic intermolecular energy potentials. An expression has been obtained to describe the cage effect of free radicals escaped into the bulk as a function of the order parameter of a nematic matrix.