After we induced resistance to docetaxel in DU-145 and 22Rv1 prostate cancer cell lines, we demonstrated that combining docetaxel with ritonavir is synergistic in docetaxel-resistant cell lines and reverses resistance to docetaxel most likely by P-gp-mediated inhibition of docetaxel efflux. The gene discussed is PGP; the disease is prostate carcinoma.