Matrix vesicles (MVs) are involved in the initial step of mineralization in skeletal tissues and provide an easily model to analyze the hydroxyapatite (HA) formation. Sr stimulates bone formation and its effect was tested on MVs. Sr2+ (15-50 mu M) in the mineralization medium containing MVs, 2 mM Ca2+ and 3.42 mM P-i, retarded HA formation. Sr2+ (1-5 mM) in the same medium-induced other types of mineral than HA and cancelled the ATP-, ADP- or PPi-induced retardation in the mineral formation. Our findings suggest that the beneficial effect of Sr2+ at a low dose (15-50 mu M) is rather an inhibitor of bone resorption than an activator of mineral formation, while at high Sr2+ concentration (1-5 mM), mineral formation, especially other types of mineral than HA, is favored. (c) 2008 Elsevier Inc. All rights reserved.