1. Volunteers have been immunized with the purified specific antigen of Type V Shigella paradysenteriae (Flexner). The subjects developed a high titer of bacterial agglutinins and mouse-protective antibodies. The agglutinin titer fell moderately after a period of 6 months. The subjects responded fairly well to a small recall dose of the antigen.
2. Two individuals from a group of 10 injected with the specific polysaccharide obtained from Type V organisms responded with an increase in bacterial agglutinins. Mouse-protective antibodies were demonstrable in the one serum tested.