We studied changes in C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) to establish normal values after uncomplicated anterior cruciate ligament (ACL) reconstruction. The levels of CRP and ESR were determined by serial measurements in 45 consecutively treated patients. Blood samples were collected before surgery and on postoperative days 1, 3, 7, 15, and 30. Both ESR and CRP showed a marked increase postoperatively, peaking between the 3rd and 7th postoperative days, the latter showing a faster return to normal ( P=0.286). These data show that CRP can be used as a more accurate predictor than ESR of postoperative complications if the blood level remains elevated or unexpectedly rises.