Several human heme oxygenase-1 promoter-driven chloramphenicol acetyltransferase constructs were examined in order to analyze promoter activity of the heme oxygenase-1 gene in microvessel endothelial cells. Heme oxygenase promoter activity was up-regulated by interleukin-6. This induction was shown to be down-regulated by glucocorticoids. Chloramphenicol acetyltransferase assays revealed that the promoter region (56 base pair) between -180 and -120 was responsible for up-regulation by growth factors, as well as for glucocorticoid-directed down-regulation. The same DNA fragments was shown to bind nuclear factor(s) from endothelial cells treated with dexamethasone. Formation of DNA protein complexes peaked after a 6-hour treatment. The DNA fragment was found to contain a sequence recognized by the STAT 3/acute phase response factor.