Prostate cancer is the most common male malignancy in the United States as well as in many European countries. It is curable as long as it is localized, but the invasion of prostate cancer and formation of metastasis turn it into a life-threatening disease. Urokinase-type plasminogen activator (uPA) is believed to play a key role in tissue degradation and cell migration under various normal and pathological conditions, including cancer invasion and metastasis. Increased expression of uPA has been reported in various malignancies including prostate cancer. However, the mechanisms of the overexpression have remained poorly understood. Here, we report increased copy number of uPA gene in 3 of 13 hormone-refractory prostate carcinomas, including 1 high-level amplification. Real-time quantitative reverse transcription-PCR showed that the increased expression of uPA coincided with the amplification of the gene in these tumors. Matrigel invasion assay showed that prostate cancer cell line PC-3, containing amplification of the uPA gene, was more sensitive to the urokinase inhibitor, amiloride, than DU145 or LNCaP cell lines, which do not have the amplification. The findings suggest that one of the mechanisms underlying the overexpression of the uPA is the amplification of the gene, which is associated with the increased invasive potential of the cells.