The prognosis for patients with metastasized prostate cancer is still poor, despite conventional aggressive therapeutic modalities. Several in vitro studies together with animal models and epidemiological studies have indicated that phytochemicals can be antitumorigenic and may be protective against human cancers. However, the potential antitumor effects of genistein isoflavone, a widely studied nutrient phytochemical, have been equivocal. In this study, we investigated the effects of genistein-selenium (Gn-Se) combination on chemosensitivity and matrix metalloproteinase-2 (MMP-2) expression levels in PC3 (hormone-independent) and LNCaP (hormone-dependent) prostate cancer cells. 3-(4,5-Dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium staining and ATP bioassay showed that genistein, selenium, and Gn-Se combination significantly inhibited growth of LNCaP and PC3 cells in a dose- and timedependent manner, independent of hormonal status, and with no significant differences in chemosensitivity between LNCaP and PC3. Gn-Se combination induced significantly the greatest growth inhibition in both cell lines. Growth inhibition was through apoptosis induction. The treatment-induced apoptotic cascades are caspase-dependent, with evidence of an alternative non-caspase pathway(s). Treatment also induced a dose- and time-dependent decrease in MMP-2 expression levels in PC3 and LNCaP with no significant differences between the two cells. Gn-Se combination induced the greatest depression in MMP-2. Overall, none of the treatment modalities had any significant inhibitory effect in normal prostate epithelial cells. The data obtained from the present study indicate that Gn-Se combination may have chemopreventive value and/or may be adjuvant to standard therapy for prostate tumors independent of hormonal status. MMP-2 expression in cancer cells has been associated with active invasion and metastasis.