Prostate cancer has become the most common cancer in males and the second most common cause of male cancer death in England and Wales. Death rates have doubled over the last 20 years. Prostate cancer is characterized by a high initial response rate to hormonal therapy. Drug-resistance is a significant cause of relapse in cancer. The multidrug resistance genes (MDR) encode resistance to a diverse family of cytotoxic chemotherapy agents. There are four known MDR genes, two of which are present in humans. MDR1 encodes for P-glycoprotein, a 170-kDa transmembrane calcium-dependent efflux pump. We examined P-glycoprotein expression by immunocytochemistry in 96 patients with prostate cancer and 20 patients with benign prostatic hypertrophy. A direct correlate was found between tumor grade, stage, and prostate specific antigen levels, indicating the possible significance of this protein in recurrent prostate cancer.