Tissue inhibitors of metalloproteinases (TIMPs) may regulate extracellular matrix turnover and cellular functions by modulating matrix metalloproteinase (MMP) activity and cell proliferation and apoptosis. To investigate the locations and functions of TIMP-4. in human breast cancer, a highly specific polyclonal anti-TIMP-4 peptide antibody (pAb-T4-S61) was developed. The potency and specificity of the purified IgG were characterized by an enzyme-linked immunosorbent assay, immunoblot, and immunohistochemistry. The optimal IgG concentration range was 0.1-10 μg/ml. pAb-T4-S61 did not cross-react with TIMP-1 and TIMP-2 and should not react with TIMP-3 according to the sequence analysis. Parental MDA-MB-435 breast cancer cells were TIMP-4 negative and a TIMP-4 transfected clone, TIMP-4-435-12, produced TIMP-4. Membrane type-1 MMP was detected although TIMP-2 was not found in these cells. Interestingly, the TIMP-4 protein was detected by immunohistochemical staining in infiltrating breast carcinoma cells in tumor tissues. Thus, pAb-T4-S61 is a useful tool to investigate expression patterns and functions of TIMP-4 in cancers. © 2001 Academic Press.