Abstract
In 1899, Metchnikoff proposed that macrophages might be studied using antimacrophage serum. The farsighted nature of this idea is indicated by the fact that virtually all the current methods for the study of lymphocyte surface receptors for antigen involve the use of antireceptor antisera. This somewhat circular approach (i.e., the use of antibodies to study antibodies) may be regarded as an example of the value of those methods of analysis which exploit biochemical affinities rather than classical chemistry.