Standard chemotherapy for pancreatic carcinoma is based on the use of gemcitabine. The clinical benefit of interferon-alpha (IFN-alpha) in advanced pancreatic cancer has been shown. However, it has been demonstrated that to be effective, there is a need for a constant amount of IFN-alpha at the site of the tumor. Therefore, we examined transfection of the human pancreatic cancer cell line DAN-G with a retrovirus encoding for IFN-alpha and the effect of IFN-alpha gene expression alone or in combination with gemcitabine on growth inhibition of DAN-G pancreatic cancer cells in vitro and in vivo in orthotopically implanted DAN-G cells in nude mice. DAN-G cells could be efficiently transfected retrovirally by the human IFN-alpha gene and significantly enhanced the levels of IFN-alpha mRNA. In vitro gemcitabine led to an alteration of G1/S phase progression in transduced as well as untransduced cells, whereas IFN-alpha led to a significant decrease in cell viability in the transduced cells via delay in the progression of the S phase but no alteration of G1/S phase progression. In vivo, tumor volume in mice was reduced significantly with gemcitabine combined with IFN-alpha (76% +/- 8.3%) compared with gemcitabine alone (62.9% +/- 7.3%) or IFN-alpha alone (24.4% +/- 5.2%) compared with untreated animals. We conclude that gemcitabine and IFN-alpha concomitantly inhibited tumor cell proliferation significantly.