These studies are a continuation of an indepth investigation into the thymus-derived-lymphocyte (T cell), its antigen receptor, and its products. Continuously propagable cloned T cell lines have been established in the course of this work by hybridizing enriched populations of murine antigen-specific T cells with BW 5147, a T lymphoma. Additional hybrids will be prepared with 5 different T cell subsets and various T lymphomas. New selection techniques will be devised. An antigen binding substance from a T cell hybrid will be analyzed as will its cellular regulation. Products and activities from new T cell hybrids will be studied.