Osteopenia develops in experimental animals following surgical removal of the ovaries (ovariectomy. Ovx) or the stomach (gastrectomy, Gx). Though the effect of Ovx has been ascribed to estrogen deficiency, the mechanism behind the Gx-evoked osteopenia remains unknown. In order to compare Gx- and Ovx-evoked osteopenia, young female rats were subjected to Ovx, gx, the combination of ovx and Gx, or sham operation (SHAM). Serum osteoclast-derived tartrate-resistant acid phosphatase 5b was measured as an index of bone resorption, and serum osteocalcin as an index of bone formation/turnover. Bone resorption predominated over bone formation during the first 4 days after Ovx but not later. Bone resorption predominated over bone formation throughout the first 4-week period after Gx. the changes were not additive in the ovx+Gx group. Transillumination and histomorphometry of the calvariae revealed extensive osteopenia in the Gx and the Ovx+Gx groups but not in the Ovx group. Peripheral quantitative computerized tomography of the femur metaphysis showed a decrease in the trabecular bone mineral density (BMD) in all three groups although Ovx+Gx seemed to induce greater trabecular bone loss than Gx alone. However, dual energy X-ray absorptiometry (DXA) of the intact femurs revealed reduced bone mineral content (BMC) in the Gx and Ovx+Gx groups but not in the Ovx group. Indeed, cortical bone was impaired by Gx and Ovx+Gx but not by Ovx. Hence, it seems clear that the Gx-evoked osteopenia differs from that induced by Ovx but that the osteopenia induced by Ovx+Gx is only marginally greater than that induced by Gx alone.