The authors elaborated a method of determination of the antimicrobial immunity intensity in diphtheria in an acute experiment: guinea pigs were infected with a virulent culture of Corynebacterium diphtheriae grown on agar with iron in a concentration depressing the toxinogenesis. A temporary absence of the toxin formation permitted to evaluate the antibacterial immunity except the antitoxic one. Guinea pigs preimmunized with somatic Corynebacterium diphtheriae antigen or an immune antimicrobial serum constituted the experimental group. The antimicrobial protection level was assessed by the difference in the mortality rate of guinea pigs in the experimental and control groups.