Interleukin-12 (IL-12) is one of the most effective cytokines for treating malignancy. Intratumoral delivery of the murine Il-12 gene, using electroporation, has been found effective in inducing regression of established tumors in mice, and more effective than intramuscular injection of this gene by electroporation, but what is not known is the molecular mechanism by which IL-12 exerts an antitumor effect. To define these candidate genes, the gene expression profiles of tumors treated with and without intratumoral Il-12 electroporation gene therapy were analyzed by cDNA array. Mig (Cxcl9), Stat1, and IRF7 are the three genes that are the most altered at the level of expression after administration of Il-12 via intratumoral electroporation, when subjected to further characterization by Northern blot, Western blot, and immunostaining. The results from Northern blot and immunostaining analyses indicate that intratumoral delivery of the murine Il-12 gene via electroporation induces accumulation of IRF7 in the nuclei of tumor cells and upregulates Mig and Stat1 expression by 15- and 5-fold, respectively, compared to intratumoral electroporation of control plasmid DNA. Intramuscular injection of the same Il-12 gene using electroporation upregulates Mig and Stat1 by only 6- and 2.9-fold, respectively, but does not induce any IRF7 accumulation in the nuclei. Further functional analyses of Mig indicate that expression in tumors can induce CD4+ but not CD8+ T cell infiltration. Further functional analysis of Stat1 indicates that a lack of Stat1 expression inhibits the Il-12-mediated induction of IP10, a known antiangiogenic gene. These data suggest that these three genes may positively correlate with the antitumor efficacy of intratumoral Il-12 electroporation gene therapy.