We analyze two analytical solutions for the study of the propagation of the four-wave mixing (FWM) signal in a strongly driven two-level system, when the stochastic effects of the solvent are explicitly considered. The first solution is valid only for a constant pump intensity, while the second solution considers pump propagation explicitly. In both cases, we were able to derive analytical expressions for the FWM nonlinear intensity signal in terms of the field amplitude and thermal noise parameters. © 2000 Academic Press.