Enzyme immunoassay studies revealed increased content of matrix metalloproteinases 2, 3 and 13 in tumors compared to the adjacent histologically unchanged mucosa in 70-90% patients with colorectal cancer, while the increase in the content of type 2 metalloproteinase tissue inhibitor did not reach the level of statistic significance. Plasma concentrations of these proteins did not correlate with the corresponding values in the tumors and did not surpass the normal levels, while their decrease after removal of the primary tumor was observed only in patients with initially high levels of this parameter.