A recombinant retroviral vector pNTK expressing the "suicide" gene herpes simplex virus thymidine kinase (HSV-TK) gene was constructed. The recombinant vector was packaged by PA317 cells and viral supernatant was used to infect the human pancreatic carcinoma cell line PC-2. After selection in G418, resistant colonies were identified and isolated. Cytotoxic effects of the non-toxic prodrug Acyclovir (ACV) or Ganciclovir (GCV) to the NTK transformant PC-2 cells was more than 90%, while that of the control PC-2 cells was less that 10%. Furthermore, the "bystander effect" of HSV-TK on PC-2 cells was also observed.