The induction of H-2-specific Ts cells was accomplished by the i.v. injection of X-irradiated (2000R) C57BL/6 spleen cells into CBA/J mice. These Ts cells significantly (78%) suppressed the delayed type hypersensitivity (DTH) response in CBA/J mice injected s.c. with X-irradiated (2000R) C57BL/6 spleen cells and given a footpad challenge with the same cell population 5 days later. We have shown that both CD4 and CD8 T cells were involved in the observed suppression, and these cells secrete T suppressor inducer (Tsfi) and T suppressor effector (Tsfe) molecules. Both Tsfi and Tsfe molecules were shown to significantly inhibit (> 87%) one-way mixed lymphocyte responses between CBA/J and mitomycin C-treated C57BL/6 spleen cells. Using an adoptive transfer method, we showed that mice given both a primary and secondary immunization with X-irradiated C57BL/6 spleen cells to induce H-2-specific Ts cells contain a significantly greater number of Ts cells than mice given only a primary immunization, suggesting the presence of memory Ts cells.