A retrovirus-mediated transduction of B-domain-deleted human blood coagulation factor VIII (FVIII-B) was attempted in partially hepatectomized rats. FVIII-B cDNA was inserted into a retroviral vector (pLNSX) and infective recombinant virus particles were produced in packaging cell lines (psi2 and PA317). Transfection of mouse NIH-3T3 cells with the FVIII-B cDNA inserted recombinant viruses, followed by G418 selection, gave a viral titer of 3.5 x 10(4) CFU/ml. FVIII-B protein, as well as FVIII-B mRNA, was detected in these cells. Transfusion of FVIII-B-expressing retrovirus particles into the tail vein of rats subjected to partial hepatectomy resulted in a relatively higher level of FVIII-B expression in liver and circulating plasma as compared with the sham-operated rats. These results indicate that the augmentation of FVIII activity in the blood of an animal by retroviral gene delivery can be enhanced by partial hepatectomy, and that the retrovirus-mediated FVIII-B cDNA delivery to regenerating liver may be an alternative method for the expression of FVIII-B cDNA in vivo.