Effects of the inhomogeneous broadening on the optical responses of a two-level system in the four-wave mixing signal (FWM) were studied in this work. In this model, we introduced in the optical Bloch equations a stochastic Bohr frequency, generated as a consequence of the solute-solvent molecular collisions. These expressions are averaged in the statistical ensemble over all realizations of the random variables. Using the convolution theorem, it is possible to incorporate the saturation effects of the electromagnetic field treated at all orders of perturbation. For the averages, we have considered two distributions of linewidth. From the analytical expressions, for both linear and nonlinear responses, numerical calculations were carried out to obtain surfaces as a function of the magnitude of the pump field and the detuning factor. Saturation effect is shown in the linear and the coupled nonlinear responses. In this work, we have already considered the inhomogeneous spectral line and studied the cases in which all the fields propagate through the medium. © 2005 Elsevier Inc. All rights reserved.