A dispersion equation is obtained for the stability of the pinch from the hydromagnetic equations supplemented by an equation for the pressure tensor of the ions. The dispersion equation is obtained for the marginal instability case only. It is observed that this dispersion equation coincides with the dispersion equation obtained from the equations of Chew, Goldberger and Low [Proc. Roy. Soc. A 236 (1956) 112] for the marginal instability case. It is concluded that the region of stability predicted from the equations that we have used is slightly more than that given by the kinetic equation used by Chandrasekhar, Kaufmann and Watson [Proc. Roy. Soc. A 245 (1958) 435].