The aim of this work was to determine sensitivity and specificity of serum pyridinoline cross-linked carboxy-terminal telopeptides of type I collagen (ICTP), a new biochemical marker of bone resorption, in order to study the rate of bone resorption associated with osteopenia development after oophorectomy in rats. The diagnostic accuracy of the bone formation marker osteocalcin (BGP) was also evaluated. Twelve-week-old female Wistar rats were used: (1) control group: sham-operated, treated with a placebo (n = 25); (2) OOX: oophorectomized rats treated with a placebo (n = 12), and (3) OE: oophorectomized rats treated with 17α-ethinyl estradiol 0.1 mg/kg/day for 3 months. The rats were sacrificed after treatment, and lumbar bone mineral density, BGP, and ICTP (serum assays specific for rat) were determined. As expected, OOX animals developed osteopenia. OOX rats showed a significant decrease (p < 0.05) in bone mineral density as compared with the control group, and OE rats showed no significant differences with respect to the control group. With respect to biochemical markers of bone remodeling, the OOX group showed a significant increase in BGP and ICTP (p < 0.005 and p < 0.05, respectively) with respect to control rats. However, the values of BGP and ICTP were similar in the OE group and in control animals. Areas under receiver operation characteristic curves corresponding to BGP and ICTP were 95 and 87%, respectively (p = 0.523). The results of the present work show that BGP and ICTP, the new resorption assay developed for rats, are reliable markers to be used in the study and follow-up of bone remodeling in OOX rats.