In the last few years a number of workers in this country have reported favorably on the use of cholesterinized antigens for Wassermann reaction. According to some reports, these so-called reinforced antigens gave even more satisfactory results than the acetone-insoluble fraction of tissue lipoids advocated by Noguchi.1 In studying the role of cholesterin in the preparation of antigen we came to the following conclusions:The apparent superiority of reinforced antigens is not due to the heightened specificity of these antigens, but to a heightened anticomplementary power of the same.In addition, cholesterol retards and, if used in sufficient connection, greatly protects the blood cells from the action of hemolytic agents, thus further increasing the tendency towards a higher percentage of positive reactions.That this influence of cholesterol is not specific is evidenced by the fact that more recently differeht authors noted the occurrence of nonspecific fixations obtained with reinforced antigen in a high ...