SUMMARYExperiments reported here demonstrate that the RT7 alloantigen and the L‐C antigen are separate and distinct structures on the surface of rat lymphocytes. The distribution of the antigens in different rat strains, including the mutant WF/fz, clearly establish the RT7 antigenic system as a polymorphic diallelic system, whereas the recognized L‐C antigenic determinatn is monomorphic and present on the lymphocytes of all strains tested. These data were obtained using monoclonal antibodies to the antigens in indirect immunoffluorescence experimenta. The two antigens were shown to redistribute (cap) independently of one another on the surface of rat thymocytes. Cells that had been exposed to anti‐L‐C antibody and FITC‐cojugated anti‐Ig followed by anti‐RT7.1 antibody and RITC‐conjugated anti‐Ig demonstrated FITC ca