This study investigated levels of complement inhibition, apoptosis of gut epithelium, and bacterial translocation (BT) associated with different doses of heparin in rats with severe burns. After burn injury, the animals in Groups 1, 2, 3, and 4 received intravenous tail-vein bolus heparin doses of 150, 300, 600, and 1200 U/kg, respectively. Group 5 received no heparin after burn injury. Group 6 served as control group. According to the results, Group 2 had the highest rate of positive staining for C3, and Group 4 had the lowest rate. There were significant differences between these two groups with respect to distribution of immunoflouresein scores for C3 (p=0.01). Group 5 had the highest mean TUNEL index of all the groups (258/10) (p=0.01). On electron microscopy, the connective tissue cells in the ileal submucosa from Groups 4 and 5 showed more significant apoptotic changes than the corresponding cells in the other groups. The total BT values in Group 4 (129 x 10(4) CFU) and Group 5 (100 x 10(4) CFU) were both significantly higher than those in the other groups (p=0.01). Group 1 had the lowest total BT value (6.1 x 10(2) CFU) (p=0.001). In summary, our results confirm that heparin administration after significant burn injury in rats can reduce BT, and that the effect is related to dose. The findings also indicate that levels of BT after burn injury increase in parallel with the extent of gut epithelial cell apoptosis.