There are many continuous and complex interactions occurring between cell surfaces and soluble, circulating molecules in the intact animal. One very important part of such molecular social behavior is the monitoring of macromolecular integrity. Although there is virtually nothing known about how the monitoring process works, it is well established that the body is capable of recognizing aged or damaged molecules and of eliminating them. Thus, molecular catabolism is a fundamental part of normal homeostasis and catabolic mechanisms are intricately involved in neoplastic, infectious and autoimmne disorders. Studies of the rates of molecular metabolism have important bearing on the role of the immune response in the aging process. Measurements of serum antibody levels are reflections of the rates of synthesis, patterns of distribution and rates of breakdown of total antibody populations. I propose to evalutate antibody metabolism (synthesis and catabolism) at the whole animal level during aging. Studies will focus on selected murine systems with particular emphasis on the catabolism of aglycosylantibodies and idiopathic paraproteins (homogeneous immunoglobulins). In addition to determining the relative degree of function of catabolic mechanisms during aging, methods are described for assaying bone marrow function and proliferative capacity and for accurately identifying and characterizing circulating paraproteins in aged animals. The objectives of these studies are to understand the functioning of catabolic mechanisms during aging, how these mechanisms are involved in the phenomenon of idiotypic paraproteinemia and the extent to which altered antibody metabolism may be involved in the aging process.