We examine several relationships that are observed in the motion of biological media in porous membrane films in the forming of a biosensor element – one of the very important bioactive composites that can be obtained by immobilizing a biological component on a porous film matrix. We study the dependence of the velocities of the motion of the front of solutions of protein molecules and viral particles in porous membrane films on the physicochemical properties of the protein molecules in various chromatographic conditions. As the solutions travel in the film there form on the polymer matrix segments with the immobilized biopolymers. The zone of immobilization of the proteins is manifested in the course of the specific color reaction that is caused by the antigens or antibodies, labeled by a ferment molecule, that are applied to these segments. It is shown that the distance of the active zone from the starting line on the porous film specimens basically depends on the molecular mass (MM) of the biopolymers participating in the reaction, on the nature of the polymer, and on the structural characteristics of the films. The relationships established in this work may be useful in creating the theoretical bases for the development of new bioactive composites.