Soluble and particulate antigens of Rickettsia orientalis were obtained by a single preparation of ether extraction of yolk-sac suspension previously treated with Amberlite XE-64. Cross-complement-fixation tests indicated that the soluble antigen has groupor species-specificity and the particulate antigen has type- or strain-specific activity. The soluble antigen was heat-labile, whereas the particulate antigen was heat-stable. Both the soluble and particulate antigens resisted trypsin and phosphatide acyl-hydrolase (phospholipase A). The soluble antigen was partially inactivated by periodic oxidation, but the particulate antigen was resistant to periodate. No change in complement-fixing titers was observed after lyophilization of the antigens. Wassermann-positive serum with high titer showed falsely positive reactions against normal yolk-sac and infected yolk-sac antigens.