Our goal is to understand how Ets family transcription factors affect the genetic programs that control bone development. Modest overexpression of Ets2 in transgenic mice leads to Down's syndrome-like bone abnormalities. We observed that in the MC3T3-E1 in vitro model of osteoblast development, mature osteoblasts have very high levels of Ets2 relative to the immature preosteoblasts. We hypothesized that overexpression of Ets2 could have noticeable effects on gene expression, and found that exogenous Ets2 expression results in a complete lack of mineralized matrix in stable Ets2 transfected cells. Our cDNA microarray-based expression profiling of preosteoblasts vs. differentiated osteoblasts revealed several genes previously unrecognized as having roles in osteoblast maturation and up-regulated only in the mature osteoblasts. The promoters of these genes and known osteoblast marker genes were examined for Ets transcription factor binding sites (EBSs). Interactions of these sites with Ets2 protein were tested by EMSA. In vitro expressed Ets2 protein was able to form a protein:DNA complex with both known (Bsp, Opn, ON) and novel (Btg2, CysC, Lum) bone-related genes. In addition, Cbfa1 was found to interact with Ets2, forming a complex on the Opn promoter.