We present a study of the polarization effects resulting from the reflection and transmission of a narrow beam of light through biological tissues. This is done numerically with a Monte Carlo method based on a transport equation which takes into account polarization of light. We will show both time-independent and time-dependent computations, and we will discuss how polarization can be used in order to obtain better images. We consider biological tissues that can be modeled as continuous media varying randomly in space, containing inhomogeneities, with no sharp boundaries.