Experiments were performed on white mice poisoned with the total antigen of Flexner dysentery bacilli. The detoxicating effect of chlortetracycline, oxytetracycline and tetracycline was demostrated both in oral and in intramuscular administration. A suitable dose of antibiotics prevented the degeneration of the cells of the central nervous system as well as the inflammatory changes in the intestines and the severe hemodynamic disturbances observed in the majority of untreated animals in dysentery intoxication. In treatment with tetracyclines the action is detoxicating manifested in the animals before the development of pronounced morphological changes in the central nervous system. This effect of tetracyclines is not caused by the neutralization of the toxin as a result of direct binding, nor by the action of the antibiotics on the bacteriemia (the latter, as shown by the authors'' experiments does not developed in these conditions). Other antibiotics (penicillin, streptomycin and colimycin) had no detoxicating effect in analogous conditions.