Previous studies in this laboratory have demonstrated that exposure of mice to the carcinogenic polycyclic aromatic hydrocarbon, 7,12-dimethylbenz[a]anthrance (DMBA) results in suppression of cell-mediated immunity (CMI), specifically the ability to generate cytotoxic T cells. This is accompanied by an increased susceptibility to challenge with transplantable tumors. Our previous studies have demonstrated no appreciable change in the composition of splenic lymphocyte populations following exposure to DMBA, suggesting a modulation of lymphocyte function, probably at the level of the T lymphocyte. The purpose of this study was to examine the mechanism of DMBA-induced T lymphocyte dysfunction following DMBA exposure, and to determine whether CTL function could be reconstituted by the addition of untreated lymphocytes or lymphokines. Exposure to DMBA in vivo at doses of 50 and 100 micrograms/g and in vitro at doses of 20 and 40 microM suppressed the ability of splenic lymphocytes to generate cytotoxic T-lymphocytes (CTL). CTL-mediated lysis of allogeneic tumor target cells could be restored by the addition of 20% T cell-enriched naive lymphocytes and by 10% T-helper cell-enriched lymphocytes. DMBA suppressed splenocyte production of the lymphokine interleukin-2 (IL-2) in response to mitogenic or allogeneic stimulation by greater than 70% following in vitro exposure and greater than 45% following in vivo exposure. Although DMBA-exposed lymphocytes were impaired in their ability to produce IL-2, CTL responsiveness could be reconstituted by the addition of exogenous IL-2 (purified or recombinant DNA-produced). Complete restoration of CTL responsiveness by the addition of exogenous IL-2 suggests that the T-helper cell, rather than the T-cytotoxic cell, is the target for the DMBA-induced CMI lesion.