Our aim was to determine whether calpain protease activity is increased in liver tissue from allografts that have poor graft function postoperatively. Liver tissue was obtained from 36 patients at 1 hr after recirculation. The patients were divided into two groups: (1) 30 patients with good graft function; and (2) six patients with immediate poor graft function. Calpain protease activity was increased 1.6-fold in biopsy specimens from patients with immediate poor function as compared with those with excellent graft function. There was no difference between the two groups with regard to cold ischemic time for organ storage, donor age, recipient age, United Network for Organ Sharing status of the recipient, or fatty infiltration of the donor liver. In summary, enhanced calpain protease activity present in the liver 1 hr after reperfusion is a risk factor for graft dysfunction.