To evaluate the surgical stress of transplantation, resting energy expenditure (REE) and 24-hour urinary urea nitrogen (UUN) were measured in 11 patients with end-stage liver disease (ELD) before and after liver transplantation. Predicted mean basal energy expenditure as determined by the Harris-Benedict equation was 860 +/- 110 kcal/m2/day. Pretransplant mean REE was 930 +/- 130 kcal/m2/day versus 920 +/- 190 kcal/m2/day in the posttransplant period (p = NS). Pretransplant mean UUN was 7.7 +/- 3.5 gm/day versus 12.9 +/- 4.4 gm/day in the posttransplant period (p less than 0.05). It is concluded that the patients in the early period after liver transplantation are hypercatabolic (increased tissue breakdown) but not hypermetabolic (increased REE) when compared with their stable state before transplantation.