We studied the changes in serum C-reactive protein levels (CRP) and erythrocyte sedimentation rates (ESR) in patients with primary osteoarthritis, who underwent uncomplicated arthroplasty. Of the 28 patients studied, 12 had cementless total hip replacement (THR), and 16 underwent cemented total knee replacement (TKR) with a tourniquet. In both groups serum CRP levels increased rapidly after surgery, peaking on day 2 (THR 23.17 mg/dl, TKR 26.02 mg/dl), and dropping gradually to pre-operative values on day 21 in THR patients and at the end of the second month in TKR patients. ESR peaked on day 5 after operation (THR 100.5 mm/h, TKR 101.3 mm/h), dropping close to pre-operative values at the end of the third month in THR patients and at the end of the ninth month in TKR patients, although, even after a year, ESRs were slightly above their pre-operative values. Serum CRP levels changed more rapidly than ESRs and returned to normal more rapidly. CRP and ESR values tended to be higher in TKR than in THR patients.