The objectives of this proposal are: 1) to map and chemically characterize the alloantigenic determinants of HLA-ABC and -DR antigens by isolating and characterizing mutants in cultured lymphoid cell lines with defined alterations in those molecules; 2) to map the determinants involved in the HLA restriction phenomenon observed in T-cell cell killing of virally infected human cells; 3) to continue to characterize and quantify mechanisms of genetic variation and effects of mutagens in human somatic cells by using HLA variants of dipolid cells; and 4) to elucidate the genetic organization of the HLA region using cloned HLA genes and deletion variants.