Current data suggest that the combination of IL-2 plus IL-6 or IL-4 supports the generation of a CTL response. In this report, we investigated whether IL-7 alone or in combination with other lymphokines supports the generation of active CTL from murine thymocytes. Added alone, IL-7 produced a modest CTL response, and this response was augmented (more than an additive response) by the addition of either IL-2, IL-6, or IL-4. After culture with IL-7, the removal of CD8+ cells correlated with a marked decrease in killing, whereas removal of the CD4+ population resulted in an enhanced CTL response. IL-7 generated a proliferative response to which the addition of other lymphokines resulted in an additive increase at best. To determine if the CTL response was found with IL-7 was dependent on the presence of endogenous lymphokines, we added blocking mAb and found that anti-IL-2 or anti-IL-6 blocked the level of CTL generated in the presence of IL-7. In contrast, anti-IL-4 was unable to inhibit CTL generation. The effect of the mAb on proliferation was somewhat paradoxical. The addition of anti-IL-2, anti-IL-6, or anti-IL-4 to cultures containing IL-7 all caused a significant decrease in proliferation that was overcome by the addition of the corresponding human lymphokines for IL-2 and IL-6. If thymocytes were fractionated and then cultured in the presence of IL-7, the double negative population gave the greatest proliferative response, the single positive thymocytes gave a response that was approximately 40% less, and the double positive thymocytes did not proliferate. These data indicate that IL-7 supports the induction of a cytotoxic response, however, this appears to require the presence of both IL-2 and IL-6.