It has been well established that all-trans-retinoic acid (ATRA) influences bone metabolism when given in the treatment or prevention of cancer. However, the molecular mechanisms underlying this are unknown. In the present Study, we investigated the effect of ATRA on differentiation of rat bone marrow stromal cells (BMSCs). BMSCs were harvested from rats and induced to differentiate in the presence or absence of ATRA in either osteogenic (OM) or control medium (CM). BMSCs underwent osteogenic differentiation, showed alkaline phosphatase (ALP) activity, a high level of matrix mineralization, and expressed osteonectin when cultured in OM. Although ATRA induced ALP activity, it failed to induce matrix mineralization and osteonectin, decrease mineralization in OM, and induce lipid accumulation in BMSCs. Moreover, while ATRA induced the expression of BMP-RIA, both BMP-RII and Smad5 mRNA were induced by OM and ATRA. Thus, ATRA inhibited osteogenesis and promoted adipogenesis of BMSCs. BMP signaling cooperated with ATRA in the differentiation of BMSCs. (C) 2008 Elsevier Inc. All rights reserved.