Reduced-size liver grafts from related donors may not be of an optimal size for adequate function in the recipient. Therefore, liver-graft regeneration is clinically important. We evaluated liver regeneration by liver-volume determinations with serial computed tomography scans in four recipients (aged 9 months to 12 years) and their donors (all fathers of the recipients) after living-related liver transplantation. Standard liver volume was calculated from the recipient's body-surface area. In each recipient, the size of the transplanted liver tended to converge to the standard liver volume with time, regardless of whether initial liver-graft volume was smaller or larger than standard liver volume. In addition, transplanted liver in the recipient regenerated much faster than remnant liver in the donor, even though both consisted of the same hepatocytes, which suggests that regeneration is regulated mainly by factors other than the hepatocytes themselves.