The aim of this study was to evaluate the changes of biochemical markers during fracture healing in patients with osteoporosis. The study included 26 patients; 9 underwent hip hemiarthroplasty (mean age +/- SD: 71.0 +/- 10.2 years, group EN) for femoral neck fractures. 7 underwent osteosynthesis (75.3 +/- 8.2 years, group OS) for trochanteric fractures, and 10 subjects had spinal compression fractures (68.2 +/- 12.0 years, group CO). No operative procedures were performed in group CO. Urinary pyridinoline (Pyr), deoxypyridinoline (Dpyr) by high performance liquid chromatography (HPLC), Crosslaps by both enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay (RIA) (CTx-ELISA and CTx-RIA) and serum N-terminal mid-fragment osteocalcin (OCN-Mid) by ELISA were analyzed at the time of admission and at weeks 1, 2, 4, 8 and 24 after operation or, in the case of group CO, after admission. As a whole, bone resorption markers started to increase from week 1, with various peak values between weeks 4 and 8 depending upon the particular marker, but returned to the initial vales at week 24. OCN-Mid started to increase from week 8 and remained at elevated levels at week 24. In groups EN and OS, bone resorption markers changed in the same manner as they did as a whole group. OCN-Mid did not change in group EN, although it increased significantly from week 8 in group OS. No biochemical markers changed significantly in group CO. In conclusion, bone resorption was accelerated at an early stage due to acute osteonecrosis or bed rest, followed by bone formation due to callus or mechanical stress later on. As far as bone resorption markers are concerned, 24 weeks are enough to eliminate the effect of fracture.