The relationship between bone formation markers osteocalcin (OC) and bone-specific alkaline phosphatase (bALP) and age in postmenopausal women was investigated. Forty-eight osteoporotic women (median age 62, range 49-76 years) were enrolled in the study. There were 17 (35%) patients aged 49-59 years (Group A), and 31 (65%) patients aged over 59 years (Group B). Parathyroid hormone, calcium, and creatinine serum levels did not differ significantly between groups. Compared with Group A, patients in Group B had higher levels of both OC (28.5 +/- 17.8 versus 46.2 +/- 19.3 ng/mL; P= 0.003) and bALP (57.3 +/- 12.4 versus 66.4 +/- 8.7 U/L; P= 0.005). A significant relationship between age and both OC (R= 0.49, P= 0.002) and bALP (R= 0.41, P= 0.009) was found only in Group B, but there was no relationship with bone mineral density. In conclusion, in postmenopausal women the increase of bone formation markers later in life may be an expression of increased bone turnover, which is partially the cause of osteoporosis.