The proposal by Lynden-Bell that violently changing gravitational fields serve as the primary mechanism of relaxation in a galaxy of stars is reexamined for disk galaxies. The point of view adopted is that the only relaxation mechanism operative for stars in the early life of such galaxies is an axisymmetric form of the Jeans instability discussed by Toomre. The most probable form of the distribution function which results for a disk of infinitesimal thickness is obtained from statistical considerations. An asymptotic method of solution based on this distribution is developed for the construction of galactic models from observed rotation curves. The distribution of stars with low peculiar velocities follows Schwarzschild’s law whereas that of stars with high velocities shows the asymmetry in galactic longitude discussed by Oort.