The growth and differentiation of macrophages is controlled by the macrophage colony-stimulating factor (CSF-1). The CSF-1 receptor is expressed in all cells of the macrophage lineage. We have used the CSF-1R promoter to drive expression of the green fluorescent protein (EGFP) in macrophages to produce the so-called MacGreen mice. The sections below contain images of the distribution of EGFP in adult and embryonic tissues of MacGreen mice (Sasmono, et al. (2003). Blood. 101:1155-1163 ) . The pattern of EGFP expression is very consistent in independent transgenic mouse lines. We have developed a series of transgenic animals tools based upon the use of the CSF-1R promoter to allow macrophage-specific gene targetting and constitutive or inducible transgene over -expression of genes of interest. We welcome collaborative interactions based upon the use of these tools.