The stability of an arbitrary system is ordinarily determined by means of the variation in its potential energy produced by a displacement of the system from the equilibrium position. In some cases, however, the investigation of stability may be more convenient if it is based on the variation in kinetic energy during a motion of the system past the equilibrium position. In this work it is shown that for magnetohydrodynamic systems such a ``dynamical'' method enables us to very simply obtain a stability criterion equivalent to the well‐known energy principle for the stability of such systems. The proposed method also permits derivation of the criterion of Kruskal and Oberman, who investigated the stability of a plasma on the basis of the kinetic equation in the limit as (m/e) → 0. In this connection it turns out to be superfluous to require the various constants of the motion [of the form ∫dvdV G(L, &mgr;,f)] to be equal to their equilibrium values, as Kruskal and Oberman did.