The determination of bone alkaline phosphatase (bAR) by IRMA and the measure of intact osteocalcin (BGP) andlor different fragments by IRMA and/or RIA are new commercially available methods for the evaluation of osteoblast activity. The aim of this work was to study the possible correlation among serum bAR and levels of BGP measured by two different methods: an IRMA which only detects intact-BGP and a RIA which detects intact-BGP and carboxyterminal fragments (C-terminal BGP) in healthy postmenopausal control women and in a group of patients with postmenopausal osteoporosis. Serum samples from 42 consecutive osteoporotic postmenopausal women, aged 62 11 years, between 39-76, and 14 control women age matched, were drawn after an overnight fasting. Levels of total alkaline phosphatase (AR), bAR, intact BGP, and intact BGP and carboxy terminal fragments were measured. In both groups we found a significant linear correlation between the levels of AP and bAP (r = 0.79, p <0.001) and intact-BGP and C-terminal BGP (r = 0.97, p