Although aromatic hydrocarbons have been extensively studied with regard to tumor formation, there has been little investigation into effects of these environmental chemicals on regulation of genes involved in tumor invasion. We investigated effects of three arylhydrocarbons on expression of MMP-9 in PC-3 and DU145 human prostate cancer cells. TCDD exposure lead to dose and time dependent increases in MMP-9 expression. Benzo(a)pyrene and a PAH-containing soot (BDS) also induced this MMP. These hydrocarbons also stimulated MMP-9 protein secretion. Our data demonstrate that aryl hydrocarbons can stimulate the production of MMP-9 in human prostate cancer cells.