We plan to employ two powerful new methodologies, hybridomas to produce monoclonal antibodies and newly developed amino acid sequence techniques, to characterize two multigene families of the mouse, those encoding the antibody molecules and Ia antigens. These analyses should provide insights into the organization, expression and evolution of these two gene families. We have recently isolated a mouse transplantation antigen by employing a monoclonal antibody produced by a hybridoma. Because of a series of improvements in instrumentation and the chemistry of microsequencing, we have been able to determine the sequence of the N-terminal 20 residues of the transplantation antigen without employing radiolabelling techniques. We hope to increase our current sensitivity (e.g. approximately 40 residues on 200 picomoles of polypeptide) by a factor of 10-100-fold within the next year. These new sequencing and microsequencing techniques will be applied to the analysis of antibodies and Ia antigens.