Autologous mixed lymphocyte culture (MLC) reactions were studied utilizing autologous purified B cells and autologous established B lymphoid cell lines as stimulating cells. Similar results were obtained although somewhat greater stimulation of lymphocyte proliferation was found with the autologous lymphoid cell lines. Cytotoxic T cells were not generated against the stimulating cells in either case when peripheral blood cells were used as targets. A low cytotoxicity was detected when lymphoid cell lines were used both as stimulators and target cells. However this was nonspecific and was always greater for heterologous lines than for the stimulator line. Third-party cell experiments demonstrated that the autologous reaction could serve as a proliferative stimulus for specific cytotoxic lymphocyte generation. Heat-treated allogeneic lymphocytes that alone do not stimulate proliferation ro cytotoxic T-cell generation in MLC reactions when added to the autologous system produced specific cytotoxic cells. The separation of the proliferative phase from the cytotoxic cell generation was especially striking in these experiments. Possible uses of this system for the generation of specific cytotoxic cells to other nonstimulatory cells are discussed.