Abstract In vitro osteoclast differentiation is supported by stromal cells. In order to isolate a stromal cell line that can support osteoclast differentiation, 22 cell lines were cloned from mouse bone marrow. One of these clones, TMS-14, is a line of preadipocytes that supports osteoclast-like cell formation without any bone resorbing factors; and another, TMS-12, is a line of preosteoblasts that supports osteoclast-like cell formation with bone resorbing factors such as prostaglandin E 2(PGE 2). The difference of these two lines for osteoclast formation was not related with their abilities of PGE 2production, but with the expression of osteoclast differentiation factor (ODF, also called OPGL, RANKL, and TRANCE), which detected with RT-PCR, in both cell lines. In TMS-14 cells, ODF mRNA was detected with or without PGE 2. In TMS-12 cells, ODF expression was detected in the PGE 2-treated cells alone. When TMS-14 cells were induced to undergo adipogenic differentiation in response to treatment with thiazolidinedione, a ligand and activator of peroxisome proliferator-activated receptor γ (PPARγ), the ability of TMS-14 cells to support osteoclast-like cell formation was prevented in the presence or absence of 1,25(OH) 2D 3. The gene expression of ODF in TMS-14 cells was also inhibited by treatment with thiazolidinedione. These results suggest that adipogenesis in bone marrow cells is related to the ability to support osteoclast differentiation. This is the first report of a cloned stromal cell line that can support osteoclastogenesis without the treatment with any osteotropic factors. Furthermore, this murine clonal preadipose cell line may be useful for studying senescence-dependent osteoporosis.