Experimental shigellous infection in guinea pigs and mice is accompanied by the phenomena of immunomodulation. Production of antibodies is stimulated with the primary and secondary immune response to ram erythrocytes or to Ni-antigen of typhoid bacteria. Simultaneously the suppression of the secondary immune response is observed. The immune-stimulating effect is demonstrated better on the models of shigellous keratoconjunctivitis and cystitis in guinea pigs and shigellous pneumonia in mice. Immunosuppression of the secondary response is displayed better with intraperitoneal infection of mice. The immunosuppressive action of virulent shigellas does not depend on the suppressive factor of the spleen.