The optical properties of a two-level molecular system immersed in a thermal reservoir and irradiated by an electromagnetic field were studied using the optical stochastic Bloch equations. The effect of the solvent is modeled as a stochastical shift of the system's Bohr frequency and the electromagnetic field includes both pump and probe fields. The resulting analytical expressions were studied by means of two and three dimensional graphics of the optical properties as a function of the pump-frequency detuning factor and the strength of the noise source. © 2008 World Scientific Publishing Company.