A method is proposed for determining the sizes of the pores that make the main contribution to the protein capacity. This involves constructing curves in $${\Gamma \mathord{\left/ {\vphantom {\Gamma {S_{R^\rho } }}} \right. \kern-\nulldelimiterspace} {S_{R^\rho } }}$$ ,R coordinates for several matrices in which the biopolymer is uniformly distributed over the volume and the surfaces are of the same chemical type but the materials differ in porous characteristics, in which Г is the Henry protein immobilization coefficient, sr the specific surface determined by mercury porometry as governed by the walls of pores whose radii exceed R, and ρ is the apparent density of the corresponding matrix. The value of R for which $${\Gamma \mathord{\left/ {\vphantom {\Gamma {S_{R^\rho } }}} \right. \kern-\nulldelimiterspace} {S_{R^\rho } }}$$ are the most similar for several of the carriers is the minimum size of the pores that make the main contribution to the capacity for the corresponding biocatalyst. The binding of trypsin at pH 7.0 and 25°C to aminoorganosilokhrom S-80 activated with glutaraldehyde leads to a uniform distribution over the particle volume. The main contribution to the total capacity for trypsin comes from pores whose sizes are 7–8 times the hydrodynamic diameter of the enzyme macromolecule.