[en] The effect of OK-432 a preparation of streptococcus haemolyticus, on accelerating the recovery of T lymphocyte function in mice after γ-irradiation has been studied. The result indicates that OK-432 has effects on several subpopulations of T lymphocytes. It can promote the recovery of mixed lymphocyte reaction (MLR) and delayed type hypersensitivity to allotype splenocytes in irradiated mice, increase the production of IL-2 by T_H lymphocytes and the proliferation response of splenocytes to non-specific mitogen Con A