It is presented that the newly synthesized mono- and disubstituted 2,5-dimercapto-1,3,4-thiodiazole derivatives exert immunotropic activity. This effect was evaluated by measuring plaque forming cell number, circulating immunoglobulins level, autologous rosette number, mitogenic activity and by performing popliteal lymph node assay. It is shown that intensity of immunotropic activity depends on chemical structure: mono-substituted derivatives had a strong suppressive effect, disubstituted compounds showed the variable activity. One compound of this group exerted a stimulatory effect. The tested compounds were active in popliteal lymph node assay and had no mitogenic activity.