Abstract: Estrogens are known to regulate the proliferation of breast cancer cells and to alter their cytoarchitectural and phenotypic properties, but the gene networks and pathways by which estrogenic hormones regulate these events are only partially understood. As starting point to obtain a genome-wide picture of the genes modulated by estrogens we have built a database of the genes having in their putative promoter region Estrogen-responsive Element (ERE).