In the past, the process of freezing in biological tissue was modeled using the regular energy equation for a homogeneous compound. New experimental evidence shows that in tissue the water freezes separately in the vascular system and in the cells. The freezing process is affected by the water transport between the cells and the blood vessels. A new equation was developed to model the experimental results. In this work the general equation for freezing of biological tissue will be presented together with a linearized version of the new equation. A perturbation solution is obtained for the linearized equation to illustrate the effect of the water transport on the freezing process in tissue.