Two individuals undergoing orthotopic hepatic transplantation received livers from donors who were on average 10 kg smaller than themselves based on recipient ideal body weight. As a result, the donor livers in these 2 cases were 29%-59% smaller than would be expected had the donor liver and recipient been matched ideally. The liver grafts in the recipients steadily increased in size, as determined by serial computed tomography scanning, to achieve new volumes consistent with those that would have been expected in a normal individual of the recipient's size, sex, and age. Fasting plasma levels of amino acids, glucagon, insulin, and standard liver injury tests were monitored to determine which measure best reflected the changes observed in the size of the grafts over time. No relationship between the changes observed in any of these parameters and hepatic growth was apparent. In both cases, the liver increased in volume at a rate of approximately 70 ml/day. These data demonstrate that a small-for-size liver transplanted into a larger recipient increases in size at a rate of approximately 70 ml/day until it achieves a liver volume consistent with that expected given the recipient's size, age, and sex.