To examine the distribution of intrasplenically transplanted hepatocytes, we used HBsAg-producing G7 HBV transgenic hepatocytes or cells labeled with 111In. Most hepatocytes translocated to the liver (55% +/- 7%; mean +/- S.D.); the spleen retained a smaller fraction (15% +/- 3%); and some transplanted cells localized in lungs (3%) or pancreas (1%). Transplanted hepatocytes were rapidly assimilated into the liver lobule. Morphometrical quantitation indicated that the numbers of transplanted hepatocytes in the liver at 48 hr and at 9 mo after transplantation were similar. Serum HBsAg was detected in recipients of the G7 HBV hepatocytes during the 1-yr experiment. These results indicate that a large number of hepatocytes can be reproducibly delivered to the liver by transplantation into the spleen. Transplanted hepatocytes engraft rapidly, assimilate into host liver, maintain normal function and survive permanently. Systems for safe delivery and localization of hepatocytes in the liver represent a critical step toward successfully accomplishing hepatocyte-directed gene therapy and repopulation of the acutely devastated liver.