Breakdown of basement membrane (BM) is believed to be an essential step for tumor invasion and metastases. We have previously demonstrated that matrix metalloproteinase-9 (MMP-9), the 92 kDa collagenase expression correlates with metastases in human colorectal cancer (CRC). This study explores the relationship between the 72 and 92 kDa type IV collagenase (MMP-2 and MMP-9) activities and pattern of type IV collagen expression during human colorectal tumorigenesis. Thirty-four CRC patients, including four synchronous adenomas and one synchronous liver metastases, were involved in this study. By immunohistochemical staining, type IV collagen expression was noted to be continuous in the BM of normal mucosa, adenoma and in two cases of carcinoma in situ. Limited or absent type IV collagen staining pattern was seen in 100 (19/19) and 23% (3/13) of CRC with and without metastases, respectively. By double immunostaining, MMP-9 protein expression was noted to localize within areas of limited type IV collagen staining. Similarly, type IV collagen staining was noted to be greatest in areas devoid of MMP-9 expression. Gelatin zymography detected both 92 and 72 kDa proenzyme forms in all CRC and normal mucosa extracts examined. The mean tumor/normal fold increases of the proMMP-2 and proMMP-9 enzyme forms were 1.6 ± 0.1 (mean ± SE) and 2.4 ± 0.5 in adenomas, and 2.1 ± 0.2 and 4.1 ± 0.7 in CRC, respectively. The 62 and 82 kDa bands were present in 63 (12/19) and 74% (14/19) of CRC with metastases, compared with only 20 (3/15) and 33% (5/15) of CRC without metastases, respectively. These differences were significant (P = 0.045 and P = 0.030, respectively). Our results demonstrate that loss of BM type IV collagen along with elevations in MMP-2 and MMP-9 expression, especially the activated forms, occur during colorectal tumorigenesis. Our data suggest that control of type IV collagenase activation may be beneficial in preventing human colorectal tumor progression.