Bone density measured with a densitometer suitable for use with small animals. Zoledronic acid (ZA) significantly increased the bone density of the femur and spine in rats. We found no difference between the control and methotrexate (MTX) groups. Treatment with a combination of MTX + ZA was as effective as treatment with ZA alone. Values are the mean ± standard deviation. *P < 0.05 versus computed tomography (CT) group; +P < 0.05 versus MTX group.