Antibody titers against the thermostable direct hemolysin produced by Kanagawa-phenomenon postitive strains of Vibrio parahaemolyticus (anti-hemolysin titers) in sera of patients suffering from gastroenteritis due to V. parahaemolyticus were determined. A sensitive method to determine anti-hemolysin titer in serum was developed and this method was applied to 201 control samples and to sera of 51 patients admitted to Osaka Munincipal Momoyama Hospital. It was found that the anti-hemolysin titers in sera of patients increased about 5-10 days after the admission. Apparent increase of anti-hemolysin titer was observed in 11 cases out of 33 cases examined. No relation between the increase of antihemolysin titer and the severity of gastroenteritis was observed.
