Markers of types I and III collagen turnover were measured in serial blood samples collected preoperatively and 60 days after surgery in 13 patients undergoing cemented total hip arthroplasty and 11 patients undergoing cemented total knee arthroplasty. The markers were the carboxyterminal extension peptide of type I procollagen (PICP) and the aminoterminal extension peptide of type III procollagen (PIIINP). The course of serum PICP and serum PIIINP in the two treatment groups were uniform. Serum PICP showed an initial fall on day 4, thereafter increasing up to days 14-28 and was still elevated on day 60. Serum PIIINP was increased on day 4, reaching its maximum on days 14-21, and thereafter declined but remained elevated above initial values. Serum osteocalcin, a serological marker of osteoblast activity, showed no significant changes in the two treatment groups during the observational period. We suggest that the changes in serum PICP and serum PIIINP reflect collagen formation in healing soft connective tissue 60 days after cemented hip or knee arthroplasty.