The postoperative course of the erythrocyte sedimentation rate (ESR) following total hip replacement was studied in 18 patients with delayed infections and compared with the course in 75 uncomplicated cases. Normally, the ESR returned to the preoperative level in 3--6 months, but in delayed infections it was significantly increased already during the first postoperative months, and never returned to normal levels. There was also a small but significant difference between the preoperative values in the two groups, which in women may be explained by a pre-existing infection in the hip.