This contract is for the acquisition and characterization of allosera directed toward the 'public specificities' of the major histocompatibility complex (MHC) in man. The contractor will screen sera from multiparous women against cell panels well characterized for both the private specificities of the MHC and public specificities as they are currently defined. The sera of interested will be acquired in large quantities and more completely characterized by absorption/elution studies as well as standard and antiglobulin enhanced cytotoxic techniques. Cluster analysis of cell/serum reactions will be done to more precisely define known and newly defined public specificities. At least one hundred milliliters of at least five new sera will be deposited each year by the contractor into the NIAID repository.