Between June, 1993 and January, 1995 a gelatin-sealed knitted Dacron (Gelseal) (g-G0, n = 7) and a collagen-sealed knitted Dacron graft (Hemashield) (g-H0, n = 8) were randomly implanted to 15 patients (pts) for replacement of thoracic aorta. We evaluated postoperative inflammatory responses and levels of Toxicolor and Endospecy which are the measurements of endotoxin. Five pts in g-G0 and 3 pts in g-H0 showed that a body temperature (BT) were above 37.5 degrees C on the 7th postoperative day (POD). In three of them (2 in g-G0 and 1 in g-H0), BT above 37.5 degrees C continued until POD 14 due to the bacterial infection. The other causes of elevation of BT were pleural effusion (2), pericardial effusion (1) and unknown origin (2). Patients without evidence of infection (n = 12) were divided into 2 groups (g-G: pts with Gelseal, n = 5, g-H: pts with Hemashield, n = 7). On POD3, postoperative BT in g-H was significantly higher than in g-G. And, on POD7, BT in g-G rose up more than in g-H. However, on POD14, BT decreased to the normal range in both groups. The values of WBC in g-G were slightly higher than in g-H and they became normal after POD7 in both groups. The levels of CRP in g-H were higher than in g-G after POD3 and in both groups they were still high on POD14. In terms of endotoxin., Toxicolor was already above the normal range from POD1 and decreased to the normal range after POD14. However, the level of Endospecy kept within normal range. In conclusion, Toxicolor-reactive substance elevates by using Gelseal and Hemashield. Its substance is not endotoxin. It would not be appropriate to consider that endotoxin is an origin of fever between POD7 and 14.