Tetracyclines are easily incorporated into bone; whether bone formation is impaired during this process is still a matter of debate. We therefore studied, by histomorphometry, fluorescence microscopy, and microradiography, a sample of trabecular bone from a patient with a total hip arthroplasty, treated without interruption for 3.5 years with doxycycline because of a pertrochanteric abscess. Absence of osteomalacia and a low-mineralization score of the edges of the trabeculae similar to that observed in a control group of 12 subjects suggest no interference by doxycycline with calcium deposition in bone.