Despite widespread use of the gelatin-sealed knitted Dacron prosthesis (GDP) in clinical practice owing to its zero porosity, the biological impacts of this graft are still controversial. We conducted a randomized controlled study on 50 patients undergoing abdominal aortic aneurysm repair to evaluate the inflammatory reaction to GDP (n = 25) and unsealed knitted Dacron prostheses (UDP, n = 25). There were no significant differences in the mean age, size of the aneurysm, operative time, blood loss, or transfusion requirements between the GDP and UDP groups. During the first 7 postoperative days (PODs), slight fever and leukocytosis were noticed in both groups. Significant differences in maximum body temperature, leukocyte count, and plasma C-reactive protein concentration were observed between the GDP and UDP groups on POD 14:37.2 +/- 0.5 degrees C vs 36.9 +/- 0.3 degrees C (P = 0.019), 8,151 +/- 1,788/microliters vs 6,914 +/- 1,501/microliters (P = 0.015), and 32.6 +/- 27.5 mg/l vs 19.0 +/- 15.8 mg/l (P = 0.048), respectively. By POD 21, however, there were no detectable differences in these variables. Thus, we concluded that GDP caused an inflammatory reaction in the 2nd week after implantation, but ultimately there were no significant differences from UDP by the 3rd week.