An individual mouse or rat can respond to an antigen by producing both antibody directed against the antigen and antibody directed against receptors for that antigen. Conceptually, the two antibodies are anti- antibodies to each other. Presumably, when both antibodies are formed by an individual, complexes of the antibodies are formed. Preliminary observations support this idea. The main objectives for the coming year will be to determine: 1) whether the complexes cause pathologic changes, and 2) the role of the antibodies alone and in complexes in the regulation of the two separate responses.