The relationship between malignant epithelial cell growth and the formation of tumor stroma is poorly understood. To investigate the roles of type IV collagenases/gelatinases and tissue inhibitor of metalloproteinase-1 (TIMP-1) in human breast cancer, we localized their messenger RNAs (mRNAs) in normal and malignant breast tissue. Type IV collagenase/gelatinase mRNAs were expressed at low levels by some tumor cells. High levels of TIMP-1 mRNA were found in all areas where tissue remodeling was evident, particularly in cells at the tumor-stromal interface. Small blood vessels in both the tumor and stroma were often outlined by high levels of TIMP-1 mRNA. These results indicate that TIMP-1 and type IV collagenases/gelatinases are expressed independently in breast cancer.