Previous immunolabeling studies have indicated that increased expression of the matrix metalloproteinase-2 (MMP-2) zymogen is associated with an increased Gleason score for human prostate cancer. In the accompanying paper, we have found by immunoblotting and ELISA that the MMP-2 enzyme (termed MMP-2a) is expressed in prostate cancer and that increased expression is associated with progression. Monoclonal antibodies specific for MMP-2a were used to investigate the expression of MMP-2a in human prostate tissue sections of benign and malignant cancers. Immunohistochemistry indicated that MMP-2a expression was undetectable in fetal (n = 4), benign (n = 11), and low Gleason score 4 (n = 8) tissue. MMP-2a was faintly expressed (+) in cancer assigned Gleason scores 5 (n = 20) and 6 (n = 13). In comparison, MMP-2a was expressed at an intermediate level (++) in tissues of Gleason score 7 (n = 24), and at a intense level ( to +) in tissues of score 8 (n = 48), 9 (n = 9) and 10 (n = 35) and in lymph node metastases (n = 10). These observations were confirmed by quantitative Computer Assisted Imaging Analysis. In general, MMP-2a was primarily expressed by the glandular epithelial cells, and in high Gleason score 10 specimens (n = 25/35) there was clear evidence of MMP-2a localization at the cell surface. These data suggest that increased MMP-2a expression may be associated with malignant progression and metastases.