The purpose of this paper is to report three groups of observations, dealing with the serologic diagnosis, the pathogenesis, and the serologic changes resulting from hormonal therapy of so-called autoimmune hemolytic anemia. The unique feature of this type of acquired hemolytic anemia is that patients afflicted with it produce antibodies or antibody-like substances capable of reacting with their own red blood cells. This is not in accord with the old dictum that an individual does not produce antibodies against antigens of his own tissues. Exceptions from this rule in the form of hemolysins reacting with the host's own erythrocytes in patients with hemolytic anemia have been reported early in the century.1These early observations could not be reproduced, except in isolated instances, for over 30 years, until it was found that the antibodies in question are "incomplete," by which is meant that they require special conditions to become manifest,