In solid organ transplantation, acute rejections are most frequent during the first weeks. The aim of this study was to investigate the relationship between graft reperfusion injury and later immune responses against the graft. Intragraft immune activation was routinely monitored by transplant aspiration cytology in 47 recipients of hepatic allografts. As a parameter of reperfusion quality, oxygen saturation of hemoglobin (SO2) in hepatic tissue was determined intraoperatively by a near-infrared spectroscopy. Grafts that presented aspiration cytology scores of 2 or more (i.e., more than 10% of lymphocytes activated) at 1 week after operation (group I, n = 14) were associated with a higher heterogeneity of hepatic tissue SO2 at the end of operation (coefficient of variation in 12 points 18.3 +/- 18.3%, mean +/- SD) than grafts with no or very mild intragraft immune activation (group II, n = 33, 9.2 +/- 4.2%; P < 0.01). Group I was also accompanied by higher postoperative peak glutamic oxalacetic transaminase level (corrected by graft size, P < 0.05) and higher donor age (43.9 +/- 12.9 vs. 32.6 +/- 13.9 years, P < 0.02). Heterogenous reperfusion (P < 0.01), higher peak glutamic oxalacetic transaminase level (P < 0.01), and higher donor age (P < 0.05) were also associated with clinical rejection at 1 week (n = 10), but not with later-onset rejection (n = 11). These data suggest that intragraft immune activation and clinical rejection in the early phase after hepatic engraftment are strongly influenced by graft injury, which can be recognized early after reperfusion.