  We present a linear perturbation analysis of the magnetorotational
instability in the presence of the cosmic rays. Dynamical effects of the cosmic
rays are considered by a fluid description and the diffusion of cosmic rays is
only along the magnetic field lines. We show an enhancement in the growth rate
of the unstable mode because of the existence of cosmic rays. But as the
diffusion of cosmic rays increases, we see that the growth rate decreases.
Thus, cosmic rays have a destabilizing role in the magnetorotational
instability of the accretion discs.
