Chronic excessive fluoride intake is known to be toxic and can lead to fluorosis and bone pathologies. However, the cellular mechanisms underlying NaF-induced cytotoxicity in osteoblasts are not well understood. The objectives of this study were to determine the effects of fluoride treatment on MC3T3-E1 osteoblastic cell viability, cell cycle analysis, apoptosis and the expression levels of bcl-2 family members: bcl-2 and bax. MC3T3-E1 cells were treated with 10(-5); 5 x 10(-5); 10(-4); 5 x 10(-4) and 10(-3) M NaF for up to 48 h. NaF was found to reduce cell viability in a temporal and concentration dependent manner and promote apoptosis even at low concentrations (10(-5) M). This increased apoptosis was due to alterations in the expression of both pro-apoptotic bax and anti-apoptotic bcl-2. The net result was a decrease in the bcl-2/bax ratio which was found at both the mRNA and protein levels. Furthermore, we also noted that NaF-induced S-phase arrest during the cell-cycle of MC3T3-E1 cells. These data suggest that fluoride-induced osteoblast apoptosis is mediated by direct effects of fluoride on the expression of bcl-2 family members. Crown Copyright (C) 2011 Published by Elsevier Inc. All rights reserved.