A new method has been suggested for the study of the synthesis of antibodies by isolated cells of immunized animals — indirect hemadsorption reaction. The reaction essentially consists of the fact that erythrocytes sensitized by bacterial haptens become capable of specific attachment to the surface of cells synthesizing antibodies. For sensitivity this test is not inferior to the bacterial attachment reaction and is superior to the latter with regard to specificity, particularly when the object of study is the formation of antibodies to antigens of immotile bacteria.