The levels of C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) were determined by serial measurements after four types of uncomplicated elective orthopedic surgery. The type of operations chosen for this study were total hip arthroplasty (primary, n = 109; and revisions caused by aseptic loosening, n = 9), unicondylar knee arthroplasty (n = 39), and lumbar microdiskectomy (n = 36). In all patients, CRP levels increased after surgery, reaching peak levels on the third day after hip arthroplasties (primary, 116 +/- 43 mg/l; revisions, 136 +/- 58 mg/l) and on the second day after knee arthroplasties (140 +/- 46 mg/l) and lumbar microdiskectomy (48 +/- 27 mg/l). C-reactive protein levels usually dropped to normal (less than 10 mg/l) within 21 days after surgery. No correlations were found between CRP response and the type of anesthesia, amount of bleeding, transfusion, operation time, administered drugs, age, or gender. Erythrocyte sedimentation rate increased to peak levels about five days after surgery, followed by a slow and irregular decrease. Still, 42 days after uncomplicated operations ESR often remained elevated. In conclusion, the level of CRP must be considered a better diagnostic aid for the early detection of postoperative infections than ESR. It can be assumed that the rapid decline in CRP after uncomplicated orthopedic surgery will be interrupted by a second rise or by a persisting elevated level if infectious complications occur.