Controversy exists regarding the expression of specific steroid receptor proteins and mRNA in human microvascular endometrial endothelial cells (HEECs). Thus, we studied steroid receptor expression in early passaged HEEC cultures and freshly isolated HEECs. Analysis of estrogen receptor (ER) and progesterone receptor (PR) mRNA levels was carried out with real-time quantitative RT-PCR, and the repertoire of genes activated by their respective steroid ligands was assessed by mRNA microarray analyses of 18,400 genes and expressed sequence tags. We observed that cultured and freshly isolated HEECs each express ER-beta mRNA but not ER-alpha. In addition, PR mRNA was also detectable in both HEEC sources. Microarray analysis demonstrated that treatment of HEEC cultures with either estradiol or medroxyprogesterone acetate produced differential effects on a wide variety of genes, and cluster analysis demonstrated that many of the genes are involved in intracellular signaling and enzymatic pathways. Thus, quantitative RT-PCR and microarray analyses demonstrate that HEECs express ER-beta and PR mRNA and that gene expression by HEECs is differentially regulated by treatment with estrogen or progestin.