This study was conducted to determine whether the administration of tri-iodothyronine (T3) to brain-dead donor pigs would improve hemodynamic instability, serum levels of thyroid hormones, or the outcome of transplantation of donor livers. Brain death was caused in young pigs (25-38 kg) by rapid inflation of an intracranially implanted balloon catheter. The animals were maintained on a ventilator and frequent measurements of acid/base balance, electrolytes, and glucose were made. At the end of 16 hr, livers were removed and implanted into prepared recipients. Serum-free tri-iodothyronine fell to zero at the end of 16 hr, and there was a 4-6-fold decline in free thyroxine (T4). The levels of serum reverse T3 (rT3) however, increased up to 6-fold. In animals treated with tri-iodothyronine 2 micrograms/hr, the serum levels of free T3 and T4 were not changed but the levels of serum reverse T3 (rT3) increased further. There were no apparent correlations between any hemodynamic parameter and serum thyroid hormone levels in the donors. After the liver transplants, recipients could be divided into those that survived longer than 6 days and those that did not. Although there were significant differences in the plasma levels of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase, there was no correlation between survival and whether the donor had received tri-iodothyronine. Although other hormones, including insulin and cortisol, may also be necessary, there is no indication from these studies that the administration of tri-iodothyronine to brain-dead donors of liver grafts benefits the serum hormone levels in the donors or the subsequent survival of the recipients.