DEXA (Dual Energy X-ray Absorptiometry) allows the measurement of the bone mineral independent of the soft tissue inhomogeneity by using 2 narrow energy bands among the wide X-ray spectrum. By this method, the measurement of the peri-prosthetic bone mineral density (BMD) is possible in hip replacement arthroplasty patients with a special computer program. The transverse histogram is one of the analytic methods of the program. In order to evaluate the possiblity of the transverse histogram to be used as an diagnostic tool for the loosening of the femoral stem, this computer program was applied to 39 hips of hip replacement arthroplasty in 35 patients. The patients were followed-up for an average of 6 years and 2 months (range, 1 year and 7 months-16 years) in the Department of Orthopaedic Surgery of Seoul National University Hospital. Clinical loosening of the femoral stem was highly suspected in 12 hips (4 cemented, 8 cementless). In the other 27 hips (10 cemented, 17 cementless), there was no evidence of the loosening of the stem clinically. In 15 out of a total of 39 hips, the status of the stem fixation was confirmed directly during the revision surgery. The clinical and operative findings were compared with the transverse histogram findings. The analyzed results are summarized as follows; l. In transverse histogram, the peri-prosthetic BMD showed 4 distinct patterns; two of these patterns seemed to demonstrate a good contact between the stem and the surrounding bone or bone cement. The remaining two were regarded to indicate a poor contact. 2. BMD patterns in transverse histogram were consistent with the intraoperative findings very well. 3. Especially in the interspace between stem and cement, transverse histogram seemed to give valuable information. In conclusion, the transverse histogram of the peri-prosthetic BMD checked by DEXA is regarded to have a possibility to be a valuable aid in determining whether the stem loosening is present or not.