A new zero-dimensional procedure was developed for the calculation of neutron spectra in a fast reactor. The procedure yields a good approximation to the spectrum at a given “point” in a fast reactor rather than for a larger “region.” Therefore, the procedure is especially suitable for the calculation of spectra in transition areas where other methods are very inaccurate. These close approximations to actually occurring spectra have been found to be good trial functions for the space-energy synthesis method of approximately solving the multigroup equations. The new procedure is based on an approximate flux from a 2-mode synthesis solution; high accuracy is not required for this initial flux. A single-group diffusion kernel is applied as weight function in the derivation of the zero-dimensional multigroup equations for the spectrum at a given point. Application of this procedure for two or more points yields an excellent set of trial functions for a subsequent space-energy synthesis calculation. Normally, M modes (with M > 2) are used in the second synthesis calculation. The complete synthesis procedure is therefore called “successive 2-M mode space-energy synthesis.” Application of a successive 2–3 mode synthesis to a two-region fast reactor model yielded very high accuracy when compared with a numerical multigroup (diffusion) reference solution. Two substantially different 2-mode solutions used as basis for the calculation of the new set of trial spectra gave approximately the same final accuracy. The high accuracy and the small computation time give the successive synthesis method a good chance to compete with the multigroup method either by a reduction in computation time or by an increase in accuracy through a more detailed description of the energy dependence.