OBJECTIVES: Replication-competent, vesicular stomatitis virus (VSV) has been demonstrated to be an effective oncolytic agent in a variety of malignant tumors. Cytokine gene transfer has also been used as immunomodulatory therapy for cancer. To test the use of combining these two approaches, an oncolytic VSV vector (rVSV-IL12) was designed to express the murine interleukin 12 (IL12) gene. This cytokine-carrying oncolytic virus was compared with an analogous noncytokine-carrying fusogenic virus (rVSV-F) in the treatment of murine SCC VII squamous cell carcinoma (SCC). STUDY DESIGN AND SETTING: The authors performed in vitro testing of recombinant VSV-F and recombinant VSV-IL12 in SCC cell lines. In vivo testing of multiple direct intratumoral injections of rVSV-F or rVSV-IL12 in an orthotopic floor of mouth murine model was performed. Each cell line was tested using rVSV-F or rVSV-IL12 at multiplicity of infection of 0.01. The ability of each virus to replicate was tested by real-time reverse transcriptase-polymerase chain reaction over 48 hours to determine viral copies of RNA. Cell survival was determined by MTT assay over 72 hours. IL12 expression by rVSV-IL12-treated cells was determined by enzyme-linked immunosorbent assay. RESULTS: Both viruses demonstrated similar infection efficiency, viral replication, and cytotoxicity in vitro. In an SCC VII orthotopic floor of mouth model in immunocompetent C3H/HeJ mice, multiple intratumoral injections with each virus caused a significant reduction in tumor volume when compared with saline injections alone. The rVSV-IL12-treated tumors showed a striking reduction in tumor volume when compared with rVSV-F and saline-treated tumors (P< .005). This striking reduction in tumor volume translated into a substantial survival benefit in rVSV-IL12-treated animals. No treatment-related toxicity was observed in either group. CONCLUSION/SIGNIFICANCE: rVSV-IL12 is a novel oncolytic vesicular stomatitis virus that effectively expresses IL12 and significantly enhances the treatment of head and neck murine carcinoma. Such combined oncolytic and immunomodulatory strategies hold promise in the treatment of head and neck cancers.