[en] The aim of this investigation was to compare Lyt markers and some properties of ''early'' and ''late'' macrophage migration inhibition factor (MIF) producers specific for H-2 antigens. BALB/c mice were immunized by injection of spleen cells of C57BL/6 mice, irradiated in a dose of 20 Gy (¹³⁷Cs, 7.4 Gy/min). Immune lymphocytes were irradiated on a ¹³⁷Cs apparatus in doses of 500, 1500, and 3000 rads. To study subpopulations of MIF producers cells formed in the course of secondary allogeneic stimulation were investigated. The study of radioresistance of the MIF producers showed that ''early'' and ''late'' MIF producers differ in their sensitivity to gamma-irradiation