Poly(vinyl alcohol) cryogels which ale prepared by freeze-thawing of concentrated aqueous solutions of the polymer are used as carriers for cell immobilization. Biomass entrapment causes a variation in the mechanical properties of the composites obtained. With rheological testing and scanning electron microscopy, it was shown that cells which manifested the reinforcing action in respect to the carrier resembled in their "physical behavior" simple model inorganic fillers of definite porosity. This porosity allows macromolecules of gel forming polymer to penetrate into the inner legions of the particles and promote the formation of tight contacts between the matrix and dispersed phase, such as entrapped cells in particular. The immobilized cultures and model fillers were as follows : Citrobacter intermedius, Zymomonas mobilis, and Pseudomonas sp, bacteria, Saccharomyces cerevisiae native and modified yeast cells, titanium dioxide, silica gels, and controlled pore glass.