Catecholamines (CA) and corticosterone (CS) exerted modulatory effect on the proliferative activity of splenic and thymic lymphocytes in response to mitogenic stimulation in vilro. Epinephrine (E) and norepinephrine (NE) potentiated proliferation in concentrations above 1 and 10 nmol/L, respectively, while CS showed a biphasic effect, stimulating proliferation at concentrations below 0.1 nmol/L and suppressing proliferation at concentrations above 10 nmol/L. Combination of CS with E, NE or both in an ineffective concentration of each (0.1 nmol/L ) showed stimulatory effect on the proliferative response of both splenic and thymic lympliocytes to Con A. Whole-body irradiation (WBI) of mice with 75 mGy incIeased the reactivity of splenic and thymic lymphocytes to Con A. It is reported for the first time in the present paper that the proliferative reactivity of splenic and thymic lymphocytes from low dose irradiated mice could be further increased in the presence of suboptimal concentrations of CS and E as well as suboptimal concentrations of phorbol myristate acetate (PMA ) and A23187. These findings may have significance in the mechanism of immunologic stimulation after low dose WBI Catecholamines (CA) and corticosterone (CS) exerted modulatory effect on the proliferative activity of splenic and thymic lymphocytes in response to mitogenic stimulation in vilro. Epinephrine (E) and norepinephrine (NE) potentiated proliferation in concentrations above 1 and 10 nmol / L, while CS showed a biphasic effect, stimulating proliferation at concentrations below 0.1 nmol / L and suppressing proliferation at concentrations above 10 nmol / L. Combination of CS with E, NE or both in an ineffective concentration of each (0.1 nmol / L) showed stimulatory effect on the proliferative response of both splenic and thymic lympliocytes to Con A. Whole-body irradiation (WBI) of mice with 75 mGy incIeased the reactivity of splenic and thymic lymphocytes to Con A. It is reported for the first time in the present paper that the proliferative reactivity of splenic and thymic lymphocytes from low dose irradiated mice could be further increased in the presence of suboptimal concentratio ns of CS and E as well as suboptimal concentrations of phorbol myristate acetate (PMA) and A23187. These findings may have significance in the mechanism of immunologic stimulation after low dose WBI