2-Methoxyestradiol (2-ME) has potent anti proliferative effects on cancer cells. Its utility alone or in combination with other therapies for treating prostate cancer, however, has not been fully explored. Androgendependent, independent human prostate cancer cells were examined in vivo for their response to combination therapy. Efficacy was assessed by terminal deoxynucleotide transferase-mediated dUTP nick-end labeling assay, measuring microvessel density (MVD) in excised tumors. Animals harboring hormonedependent tumors treated with 2-ME alone, androgen deprivation therapy alone, or the combination of the two had a 3.1-fold, 5.3-fold, 10.1-fold increase in apoptosis, respectively. For hormone-independent tumors, treatment with 2-ME resulted in a 2.43-fold increase in apoptosis, a 73% decrease in MVD. 2-ME was most effective against hormone-dependent tumors in vivo, combination therapy resulted in a significant increase in efficacy compared to no treatment controls, trended toward greater efficacy than either 2-ME or androgen deprivation alone. Combination therapy should be investigated further as an additional therapeutic option for early prostate cancer.