Epithelial ovarian cancer (EOC) remains localized within the peritoneal cavity in a large number of patients, lending itself to i.p. approaches of therapy. In the present study, we investigated the effect of replication-selective herpes simplex virus-1 (HSV-1) used as an oncolytic agent against EOC and the use of human teratocarcinoma PA-1 as carrier cells for i.p. therapy. HSV-1716, a replication-competent attenuated strain lacking ICP34.5, caused a direct dose-dependent oncolytic effect on EOC cells in vitro. A single i.p. administration of 5 × 10⁶ plaque-forming units resulted in a significant reduction of tumor volume and tumor spread and an increase in survival in a mouse xenograft model. PA-1 cells supported HSV replication in vitro and bound preferentially to human ovarian carcinoma surfaces compared with mesothelial surfaces in vitro and in vivo. In comparison with the administration of HSV-1716 alone, irradiated PA-1 cells, infected at two multiplicities of infection with HSV-1716 and injected i.p. at 5 × 10⁶ cells/animal, led to a significant tumor reduction in the two models tested and the significant prolongation of mean survival in one model. Histological evaluation revealed extensive necrosis in tumor areas infected by HSV-1716. Immunohistochemistry against HSV-1 revealed areas of viral infection within tumor nodules, which persisted for several weeks after treatment. Administration of HSV-infected PA-1 carrier cells resulted in larger areas of tumor infected by the virus. Our results indicate that replication-competent attenuated HSV-1 exerts a potent oncolytic effect on EOC, which may be further enhanced by the utilization of a delivery system with carrier cells, based on amplification of the viral load and possibly on preferential binding of carrier cells to tumor surfaces.