Herpes simplex virus type 1 (HSV-1) deleted for the immediate-early gene was applied for treatment of hepatoma cells of SKHep 1 and Huh-7. Hepatoma cells were cultured in medium containing HSV1 expressing GFP gene (QOZ/HG) to determine its transfection rate, and both cell lines infected by MOI 1 of QOZ/HG were found to have high expression of GFP without cytotoxicity. Subcutaneous growth of SKHep 1 cell tumor in nude mice was significantly reduced by injection of replicative-deficient herpes virus (TOZ.1) containing Tk-gene with administration of GCV, in comparison with that of noninjected tumor. SCID mice of peritonitis carcinomatosis due to Huh-7 hepatoma cells infected with TOZ.1 could survive longer under administration of GCV than those without TOZ.1. Therefore replicative-deficient HSV1 is a useful vector for treatment of human hepatoma cells, and TOZ.1 with GCV may be applied to suicide gene therapy for hepatoma and peritonitis carcinomatosis of hepatoma cells. (C) 2002 Elsevier Science (USA).