The objectives of this research are two-fold: to identify specific surface molecules of mouse and human lymphocyte subpopulations and determine their structure and biological function, and to determine the genetic and biochemical factors which control the expression of cell surface antigens. BIBLIOGRAPHIC REFERENCES: Hyman, R., and Trowbridge, I.S. (1977). Somatic genetic analysis of the surface antigens of murine lymphoid tumors. Cold Spring Harbor Symp. Quant. Biol., in press. Trowbridge, I.S., Hamilton, M., Hamilton, R., and Bevan, M.J. (1977). Preliminary characterization of two thymus-dependent lymphocyte xenoantigens from mouse. Biochem. J., in press.