Hemolytic and precipitin reaction of nucleic acid and nucloprotein fractions from Sh. flexneri 2 a and St. aureus were studied and the results as follow are obtained. 1 In these microorganisms, hemolytic reactions of nucleic acid fractions were negative, and precipitin reactions were positive. 2 Nucleoprotein fraction from Sh. flexneri 2 a grown on glucose added medea showed a stronger positive hemolytic reaction, whereas that from St. aureus tended to negative. 3 Nucleic acid fractions from these microorganisms grown on Fe⁺⁺ deficient medea by adding α, α'-dipyridyl showed a negative hemolytic reactions. 4 From these results it could be seen that the immunological properties of nucleic acid or nucleoprotein fractions were affected by the composition of culturing medea.