A method for calculating reactor lattices by means of passage probabilities taking account of scattering anisotropy is extended to the multigroup case. The computed multiplication coefficients and the power-release distribution are essentially just as accurate as the Monte Carlo values if the errors due to the effective multigroup constants are removed. Apparently, the proposed method will be more effective for determining small difference effects. ∑ ∑ in J J J J j s j s j s j s , , , , 1063-4258/05/9901-0446