[en] A two-stage operator splitting algorithm has been used to time advance the three-dimensional Fokker-Planck equation for the electron distribution function in a tokamak. In the first stage, derivatives in the two velocity-space dimensions are advanced together implicitly. Derivatives in the remaining (spatial) dimension are advanced in the second stage. The treatment is restricted to problems which are diagonal in the spatial dimension. The algorithm gives accurate solutions in modest CPU times unlike alternative schemes considered. We described the technique which includes features that accomodate the internal boundary conditions arising from trapped electron effects. (orig.)