Orthotopic implantation of human colon carcinoma cells is useful for studying the behavior of metastatic subpopulations. We observed that the parental line and variants of human colon carcinoma KM12 cells were all tumorigenic following implantation into the subcutis or cecal wall of BALB/c nude mice. Their ability to metastasize to distant organ sites varied, however, with the site of growth. Subcutaneous (SC) tumors did not produce visceral metastases, whereas cecal tumors metastasized to the regional mesenteric lymph nodes and to the liver. To examine the influence of organ environment on the extracellular matrix-degrading activity of the tumors, we inoculated human colon carcinoma cells into the subcutis or cecal wall and after 7 weeks isolated and cultured the tumors in serum-free medium. The conditioned media of SC tumors contained very low levels of type IV collagenase (gelatinase) and heparanase (heparan sulfate-specific endo-beta-D-glucuronidase), whereas the media of the cecal wall tumors contained high levels of both. Zymograms of the media revealed that the intracecal human colon carcinomas secreted more than three times the amount of latent and active forms of 92-kd type IV collagenase than did the SC tumors. Moreover, only the conditioned media of intracecal tumors contained latent and active forms of 64-kd type IV collagenase. Histochemical analysis using rabbit antiserum raised against the synthetic peptides of 72-kd procollagenase type IV showed type IV collagenase in the intracecal tumors; human colon carcinoma growing SC, however, were not stained significantly. These results suggest that factors in the organ environment may affect production and secretion of tumor extracellular matrix-degrading enzymes, and these factors may modify the metastatic behavior of human colon carcinoma cells in nude mice.