Proteolytic enzymes, such as type IV collagenase, play an important role in tumor invasion and metastasis. To examine M_r 72,000 type IV collagenase expression in human colon carcinoma, blot hybridizations of total RNA from 19 primary colon tumors were performed. These filters were probed with complementary DNA probes encoding the M_r 72,000 type IV collagenase metalloenzyme. The results were expressed as the ratio of the messenger RNA (mRNA) levels in the tumor tissue to that in the adjacent normal mucosa (R). The level of the 3.1-kilobase type IV collagenase mRNA was higher in the primary tumor than in the normal adjacent colonic mucosa in 13 of 18 (72%) cases with a diagnosis of adenocarcinoma. These cases were divided into high expression (R, 4.50 to 29.34) and intermediate expression (R, 2.54 to 3.31) subgroups. Both groups showed statistically significant (P < 0.05) elevations when compared with the five cases showing the lowest levels of M_r 72,000 type IV collagenase mRNA expression (low expression subgroup; R, 0.96 to 1.48). With this demonstrated elevation of M_r 72,000 type IV collagenase mRNA in colorectal adenocarcinoma we examined concomitant expression at the protein level using immunohistochemical techniques. Immunohistochemical examination of 70 cases of colon tumors, including 30 benign adenomas, using anti-M_r 72,000 type IV collagenase antibodies demonstrated a significant correlation with Duke's classification (P < 0.001). Our results suggest that enhanced expression of the M_r 72,000 type IV collagenase enzyme may be a marker of human colorectal tumor invasiveness.