Summary: The phosphate metabolism of spleen cell preparations has been measured by the uptake of P32 phosphate into acid soluble, fat soluble, ribonucleic acid and desoxyribonucleic acid phosphate fractions. Spleen cell preparations making antibody in vitro, after anamnestic in vivo stimulation with alum precipitated Ea, showed markedly raised uptake into all fractions, compared with nonantibody forming cells. The significance of these findings is discussed.