Stable gene transfer into hepatocytes might be used to compensate for a genetic deficiency affecting liver function or to deliver diffusible factors into the blood stream. In rats, we have combined retroviral-mediated gene transfer with a surgical procedure in which the liver is temporarily excluded from the circulation and infected in vivo. Partial hepatectomy was performed 24-48 hr before perfusion with virus to induce hepatocyte division and facilitate viral integration. A helper-free recombinant retrovirus coding for beta-galactosidase with nuclear localization was used to score cells that expressed the transgene. For at least 3 months after gene transfer, up to 5% of hepatocytes expressed nuclear beta-galactosidase. Whereas in vitro reimplantation of genetically modified hepatocytes has proved to be inefficient in stably transferring genes into the liver, our approach provides a feasible alternative.