Serum C-reactive protein (CRP) levels and erythrocyte sedimentation rates (ESR) were measured in 46 patients treated with uncomplicated primary hip replacements, 39 total tip replacements and 7 bipolar hip replacements. In uncomplicated primary hip replacements, ESR levels were slightly elevated preoperatively and were variable postoperatively. But CRP was normal before surgery and elevated in postoperative course, but back to normal within three weeks in most cases. Early success of hip arthroplasty is in indicated by normalization of CRP within three weeks, regardless of ESR. Since ESR seems to react somewhat differently from the CRP, both methods are useful in the monitoring of complications after hip arthroplasty.