Genistein (4,5,7-trihydroxyisoflavone) has been reported to induce cell cycle arrest and apoptosis in different cancer cell lines in vitro and to show antitumor activity against a variety of tumors in animal models. We have previously reported (S. A. Alhasan et al., Nutr. Cancer, 34:12-19, 1999; S. A. Alhasan et al., Int. J. Oncol., 16: 333-338, 2000) that genistein induces cell cycle arrest and apoptosis by up-regulating p21(WAF1) and Bax, and down-regulating cyclin B1 and Bcl-2 in a head and neck cancer cell line. However, the precise molecular mechanism(s) by which genistein elicits its effects on head and neck cancer cells still remains to be elucidated. In the present study, we report that genistein induces several specific molecular changes in head and neck cancer cells, such as down-regulation of c-erbB-2 expression, down-regulation of MMP-2 and MMP-9 secretion, inhibition of tumor cell invasion and down-regulation of nuclear factor-kappaB DNA binding activity. In addition, genistein inhibited the levels of phosphorylated Akt and the expression of 14-3-3 protein. Moreover, genistein induces telomere shortening in treated cells without affecting telomerase activity in vitro. We also observed that genistein inhibits the translocation of telomerase catalytic subunit [human telomerase reverse transcriptase (hTERT)] to the nucleus, which may result in telomere shortening, although the activity of telomerase is unaffected, along with the inhibition of metaphase spread of chromosomes. From these results, together with our previously published reports, (S. A. Alhasan et al., Nutr. Cancer, 34: 12-19, 1999; S. A. Alhasan et al., Int. J. Oncol., 16: 333-338, 2000) we conclude that genistein elicits pleiotropic molecular changes that resulting in the inhibition of cell growth and the induction of apoptotic cell death of head and neck cancer cells, which suggests that genistein may be useful as a chemotherapeutic and/or chemopreventive agent for head and neck cancer.