The aim of the present study was to assess the effects of the new fluorine pro-drug monofluorophosphate (MFP) in postmenopausal women with vertebral osteopenia and high bone turnover. We enrolled postmenopausal women (PMW, 43-59 years) who had had a natural menopause 2-5 years before the study, had vertebral bone mineral density (BMD) < 1 SD from the premenopausal mean, and had at least one of the biochemical markers of bone remodeling > 1 SD over the mean for premenopausal women. Patients were randomly divided into two treatment groups (group 1, 500 mg/day of oral calcium; group 2, MFP at the dose of 20 mg F-equivalents + 600 mg calcium/day) for 2 years (n = 21 in each group). The lumbar vertebral (L2-4) BMD and total body bone mineral (TBBM) were measured by dual-energy X-ray absorptiometry (Lunar DPX, Lunar Corporation, USA). Urinary hydroxyproline excretion (OH-P/Cr), plasma bone Gla protein (BGP) and serum alkaline phosphatase (AP) were assayed. In group 1 the markers of bone turnover and vertebral BMD did not show any significant modification, while TBBM showed a significant (p < 0.05) decrease after 24 months. In group 2 a significant (p < 0.05) decrease in OH-P/Cr (-23.9 +/- 2.0%), and an increase in both BGP (+19.4 +/- 2.6%) and AP (+10.3 +/- 2.6%) levels were observed after 24 months of MFP administration. In this group, both vertebral BMD (+5.01 +/- 0.9%, p < 0.01) and TBBM (+4.0 +/- 0.6%, p < 0.05) showed a significant increase after 24 months. Present results suggest that, in osteopenic PMW, MFP administration induces a significant increase in vertebral BMD without impairment of cortical bone, with a reduction in bone resorption and an increase in bone formation rate.