This report describes the in vivo and in vitro induction of murine (AChR)-specific suppressor T cells (Ts) and T cell factors (TsF), and the development of an appropriate assay system for their measurement. The assay described is based on the in vitro Mishell-Dutton culture system. Using this assay, it was shown that the AChR-specific helper cell is an Lyt-2- radiosensitive T cell. Moreover, the proliferating cell measured in the lymphocyte transformation assay was shown to provide AChR-specific T cell help. In vivo induction of Ts cells is achieved by injection of soluble AChR; potent AChR-specific suppression is found in the spleen 1 wk later. In vitro induction of Ts cells involves the primary education of naive splenocytes by culturing them with high concentrations of AChR. Both the in vivo- and in vitro-induced Ts cells were shown to secrete AChR-specific factors that mediate their suppressive effects. The possibility of specifically suppressing the AChR-immune response may be of a particular clinical importance since the AChR is the target autoantigen in the neuromuscular autoimmune disease myasthenia gravis.