A method based on a stochastic approach for space dependent nuclear reactor kinetics in one dimension. We present a method to solve analytically and numerically parabolic systems of partial differential equations appearing in the reactor physics studies of space-time neutron kinetics in multigroup diffusion theory. We use mainly stochastic differential equations associated to the equations: ∂f/∂t=∇[D∇ 0 ]· Moreover, we define the evolution operators corresponding to the different physical phenomena arising on neutron diffusion. By a process that we call “mixing”, we construct the general solution considering simultaneously all the physical phenomena. We present a computer code “MIXAGE” for one spatial dimension and two energy groups and we present some test problem solved using this code and compare the results with those obtained by other methods.