1. In experimental rabbit infections by germs of the genus Aeromonas using agglutination and complement fixation techiques antibodies formation persist for a period of several months. 2. The introduction of antigens unrelaten to these antibodies do not affect their levels. 3. The experimental reinfection induces an immunological secondary response which is manifested between the fourth and seventh days. 4. The levels of antihemolysin do not undergo any modification after the injection of homologous or heterologous antigens. 5. The persistence of antibodies during the experimental infection suggests tha they could be investigated for epidemic purposes in human and animals sera.