Three precipitating serum soluble antigens (SAg 1, SAg 2, SAg 3) were demonstrated in the serum of chickens that had been injected with Plasmodium gallinaceum 72 to 80 hours previously. These antigens were detected when the chickens were tested by double diffusion in gel against an antiserum obtained from chickens that survived the infection. The three antigens showed a molecular weight relationship of SAg 1 > SAg 2 > SAg 3 based on their diffusion in gel and elution from Sephadex G-200. They were selectively precipitated by specified concentrations of sodium sulfate and were partially resolved from DEAE-cellulose by increasing molar concentrations of phosphate buffer. SAg 1 was antigenically unrelated to SAg 2 and SAg 3. SAg 2 appeared to contain lipid, as it was precipitated by dextran sulfate.