We examined production and tissue localization of matrix metalloproteinase (MMP)-1 (tissue collagenase), MMP-2 (gelatinase A), MMP-3 (stromelysin-1), MMP-9 (gelatinase B), tissue inhibitors of metalloproteinase (TIMP)-1 and TIMP-2 in human breast carcinomas. In more than half of the cases, MMP-1, MMP-2, MMP-9, TIMP-1 and TIMP-2 were immunolocalized in carcinoma cells and MMP-2 was on the carcinoma cell membranes as well, whereas MMP-3 was positively stained in less than 15% of the cases. MMP-1 staining in carcinoma cells was significantly higher in scirrhous carcinoma than in other types of carcinoma. MMP-9 expression was remarkably higher in the carcinoma cases with lymphnode metastasis than in the non-metastatic cases. MMP-3 was mainly expressed in T-lymphocytes infiltrated in the tumor stroma. Stromal fibroblasts were positive for all these MMPs except for MMP-3. The TIMP-1 levels released into the culture media by carcinoma tissues were significantly lower than those by fibroadenoma tissues, although there were no significant differences in the levels of MMP-1, MMP-2, MMP-9 and TIMP-2. Gelatin zymographical analyses showed that the activation rate of the zymogen of MMP-2 (proMMP-2) is significantly higher in the more advanced carcinoma group with lymphnode metastasis than in the metastasis-negative and fibroadenoma groups. These data indicate that MMP-1, MMP-2 and MMP-9 are highly expressed in human breast carcinoma tissue and suggest that activation of proMMP-2 may be an indicator of lymphnode metastasis of the breast carcinoma.