Matrix metalloproteinases are considered to play an important role in tumor invasion and metastasis. To elucidate the involvement of MMP-1 in human colorectal carcinoma, we performed immunohistochemical analysis on tissues from 20 colorectal adenomas and 142 colorectal adenocarcinomas, including 27 intramucosal carcinomas and 115 invasive carcinomas. MMP-1 was not expressed in any of the 20 cases of colorectal adenoma examined. In contrast, 108 of 142 cases (76.1%) with colorectal adenocarcinoma showed immunoreactivity for MMP-1 in the carcinoma cells themselves. Expression of MMP-1 was also identified in stromal cells around the carcinoma. We investigated the relationship between pathological features in colorectal carcinoma and MMP-1 immunoreactivity of the tumor cells. MMP-1 expression was less frequent in intramucosal carcinomas and weaker than that in invasive carcinomas (P < .0001). Among the 115 cases of invasive carcinomas, MMP-1 immunoreactivity was significantly correlated with the depth grading of tumor invasion (P < .05), tumor growth pattern (P < .05), the presence of lymphatic invasion (P < .05), venous invasion (P < .05), neural invasion (P < .05), lymph node metastasis (P < .005), hepatic metastasis (P < .05), and increasing stages of Dukes' classification (P < .05). In situ hybridization, using an MMP-1 oligonucleotide probe, confirmed the presence of MMP-1 mRNA in colorectal carcinoma cells themselves. Expression of MMP-1 mRNA was detected by the reverse transcription polymerase chain reaction method in cultured human colorectal carcinoma cell lines and colon carcinoma tissue obtained at surgery. These findings suggest that the expression of MMP-1 is one of the important factors related to tumor invasion and metastasis in colorectal carcinoma.