Summary: Aqueous saline extracts of Salmonella organisms are antigenic. They elicit in rabbits the production of specific O- and H-agglutinins, of precipitins and complement-fixing antibodies. O- and H-agglutinins are similar in strength to those produced by immunization with bacterial cells; complement-fixing substances are somewhat weaker. O-antigens in the extracts are heat-stable, H-antigens are heat-labile as far as antibody production is concerned. While, as a rule, precipitins and complement-fixing antibodies were directed only against O-antigens, complement-fixation with H-antigens was observed in two instances. They involved antigen-antibody combinations that have been recorded previously.