Polymeric alpha-toxoid with a molecular weight of 450 000--600 000 was obtained by condensation of alpha-toxoid of Cl. perfringens, type A, with glutaric aldehyde. Experiments on guinea pigs showed that in the adsorbed preparations the immunogenic properties of both monomeric and polymeric alpha-toxoids are practically identical. The primary immune response after the immunization with nonadsorbed antigens was 3 times greater than that induced by the monomer. Polymerization of alpha-toxoid failed to change its thymus dependency.