Transduction efficiencies of current viral vectors are inadequate to modify a sufficient number of tumor cells to achieve a relevant antitumor response. We hypothesized that replication of adenoviral vectors in tumor cells could amplify gene transduction. Adenoviral replication could be obtained in tumor cells by delivering genes essential for virus replication. Of note, progeny virus would be replication-defective, and the availability of replication-enabling genes would limit the production of new cycles of replication. We have cotransfected into ovarian cancer cells a replication incompetent E1-deleted adenovirus expressing HSV thymidine kinase and plasmids providing E1 sequences needed for replication. Cotransfection was performed using adenovirus-polylysine conjugates. Cells were analyzed for production of new virus by titer determination in growth permissive 293 cells. Cells were similarly cotransfected in separate experiments with reporter gene plasmids. In two different ovarian carcinoma cells lines, SKOV3.ip1 and OV4, we obtained, by adding replication enabling sequences, viral titers three orders of magnitude higher than infecting only with virus. Further, differences in new virus production did not correlate with differences in transduction efficiency, as shown by reporter gene expression. To determine if new viruses maintain functionality, killing assays were performed. Lysates from cell lines showing high virus production were used to infect the same cell line populations. Half of the samples were treated with ganciclovir. Cell viability determination showed that new virus specifically induced killing in GCV-treated cells. A similar viral amplification effect could also be shown in primary ovarian cancer cells derived from patients. Thus, transcomplementation strategies can be developed to obtain replication of recombinant adenoviral vectors in ovarian tumor cells and in ovarian cancer primary cells. Importantly, the transgene of progeny virus is fully functional. This may therefore represent a strategy to overcome limited tumor transduction by current vector systems and to enhance therapeutic effects.