BACKGROUND Antiresorptive therapeutic regimens are the mainstay of current management of osteoporosis. Treatments that are promoting new bone formation are less available and less affordable. Previous studies have suggested that 24,25(OH)(2)D(3) could enhance bone formation. The effect of 24,25(OH)(2)D(3) on bone formation in ovariectomized osteopenic rats (OVX) was evaluated in this study. METHODS Mature Sabra rats were divided into two groups: sham-operated and OVX. Three months after surgery the OVX and sham-operated rats were divided into the following subgroups: (1) sham rats injected with vehicle, (2) sham rats injected with 24,25(OH)(2)D(3), (3) OVX rats injected with vehicle, and (4) OVX rats injected with 24,25(OH)(2)D(3). After 2 weeks' treatment, histomorphometry of the right tibiae was performed. RESULTS Ovariectomy resulted in a decrease in total bone volume (TBV/TV) and in bone formation (BFR/BS), P < 0.005 and P < 0.05 respectively, when compared with the sham-operated rats. Beside the decrease in TBV and BFR, the OVX rats showed an increase in osteoclastic bone resorption (P < 0.001 vs. sham). Administration of 24,25(OH)(2)D(3) was followed by an increase in all static and dynamic bone-forming parameters. The TBV/BV (P < 0.025), osteoblast surface (Ob.S/BS) (P < 0.001), as well as the BFR/BS (P < 0.005), increased in the OVX-treated group when compared with the OVX-untreated and sham-operated rats. This increment in bone formation was associated with a decrease in bone resorption (P < 0.001 in OVX-treated vs. OVX-untreated rats). CONCLUSIONS This study shows that 24,25(OH)(2)D(3) may be of benefit in experimental osteopenia following ovariectomy, both by suppressing osteoclastic hyperactivity and by stimulating bone formation.