Phosphorus metabolism in lung, spleen and kidney was investigated in connection with the virus infection. For this purpose radioactive P(32) was employed as the tracer and its incorporation and distribution were examined on three organs of the infected mouse. The mice were intracerberally inoculated and various hours after the inoculation they were intraperitoneally injected with adequate amounts of P(32). Twelve hours after the injection of P(32) each of the lung, spleen and the kidney was fractionated by Schneider's method, respectively. Acid soluble fractions, phospholipid fractions and nucleic acid-phospho protein fractions were obtained and examined on their radioactivities. Remarkable in corporation of P(32) to the nucleic acid phospho protein fractions of lung, spleen and kidney of the infected mouse was observed just at the incubation stage or the so-called visceral phase of Japanese B Encephalitis. This seems to imply that rapid metabolic changes in nucleic acid and phospho protein or other related substances take place in these organs at the visceral phase oo Japanese B Encephalitis.