In this study, we report that an interleukin-6 (IL-6)inducible E1A- substituting activity can be exploited for the production of infectious adenoviral particles during infection with the E1A-deleted adenovirus (Ad) Ad5d1312. The basal level of complementation can be increased by 1.5 log by induction of the HepG2 cells with recombinant human IL-6. Additionally, the IL-6-inducible E1A-substituting activity can complement E1A deletion in other cancer cell lines to render them Ad producer cells on induction with recombinant human IL-6, although the efficiency of complementation varies between cell lines. Ad5dl312 can replicate in, produce cytotoxic effect, and kill human tumor cells without addition of exogenous IL-6 in the context of tumor cells possessing an IL-6 autocrine arc, such as ovarian tumor cells. In contrast, normal human mesothelial cells isolated from normal human peritoneum lining do not support replication of Ad5dl312, even in the presence of exogenous IL-6. These results suggest that Ad5d1312 could be used as a cytotoxic agent to selectively kill tumor cells responsive to or possessing an IL-6 autocrine arc.