Pancreatic cancer is an aggressive, rapidly fatal disease against which current nonsurgical therapy has minimal impact. This study evaluates the efficacy of two novel, replication-competent, multimutated herpes viruses (G207 and NV1020) in an experimental model of pancreatic cancer. Four human pancreatic carcinoma cell lines were exposed to G207 or NV1020, and cell survival and viral progeny production were determined. Flank tumors in athymic mice were subjected to single or multiple injections of 1 x 10(7) G207 or NV1020, and tumor volume was evaluated over time. For all of the cell lines, G207 and NV1020 produced infection, viral replication, and cell lysis (P < 0.05). NV1020 resulted in a higher production of viral progeny compared to G207. The efficacy of viral tumor cell kill was greatest in those cells with the shortest in vitro doubling time. For flank tumors derived from hs766t, single or multiple injections of both viruses were equally effective and significantly reduced flank tumor burden (P < 0.05). Complete hs766t flank tumor eradication was achieved in 25% (5 of 20) of animals treated with G207 and 40% (8 of 20) of animals treated with NV1020. In vivo efficacy correlated with in vivo tumor doubling time. There were no adverse effects related to viral administration observed in any animal. NV1020 and G207 effectively infect and kill human pancreatic cancer cells in vitro and in vivo. Given the lack of effective nonoperative treatments for pancreatic cancer, oncolytic herpes viruses should be considered for clinical evaluation.