We established a differentiation-inducible preadipocyte cell line, designated A54 preadipocytes, from C3H10T1/2 (10T1/2) mouse embryo fibroblasts. A54 preadipocytes had marked hematopoiesis-supporting ability in vitro but this ability was lost after terminal differentiation to adipocytes. In this study, to identify molecules that contribute to the hematopoiesis-supporting ability of A54 preadipocytes, we screened genes that were differentially expressed in A54 preadipocytes and isolated seven novel genes by reverse transcriptase polymerase chain reaction mRNA differential display. An RNase protection assay confirmed that one of these genes was expressed at high levels in parent 10T1/2 cells and A54 preadipocytes but to a much lesser extent in fully differentiated A54 adipocytes. This gene was defined as a gene that was downregulated during adipocyte differentiation-1 (drad-1). The size of drad-1 mRNA was 8.2 kb, and the gene was expressed in other mouse preadipocytes, namely, ST2 and PA6 cells, that have hematopoiesis-supporting ability. Moreover, drad-1 was also found to be expressed in bone marrow in vivo. The function of the protein encoded by drad-1 is unknown, but the expression of the gene may be useful as a molecular marker of adipocyte differentiation.