Abstract This study demonstrates for the first time that mucin gene expression can be significantly up-regulated by steroid hormones. The effects of estrogen, progesterone and dexamethasone on the expression of three mucin genes, MUC1, MUC4 and MUC5c were determined in a human epithelial cell line. This cell line secretes mucin and contains steroid receptors. Steady-state mRNA levers were quantified by slot blot hybridization using radiolabelled oligonucleotide probes. Normally, these genes (originally isolated from airways) are expressed at low constitutive levels. However, steady state levels of MUC4 and MUC5c mRNA were up-regulated at least 3-4 fold by estrogen supplementation, and 1.5-2 fold by dexamethasone. MUC1 mRNA levels were minimally affected. Progesterone supplementation had no effect but was able to interfere with the up-regulation by estrogen. The mechanism of regulation remains to be determined but may be transcriptional. However, steroids have been shown to control gene expression at several different levels.