The observed solid is infinite, homogeneous and has a linear constitutive equation for stress. It is assumed that this body contains a finite very large number of lines of infinitely long mutually parallel helical dislocations. Then the method of statistical hydrodynamics was applied to the dynamics of discrete dislocations. The resulting system of field equations is complete so that the problem of determining the dislocation density, dislocation velocity, elastic distortion field and velocity field can be solved if the initial conditions are given. This procedure can also be applied to more complicated arrangements of dislocation lines and loops.