We investigated the matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinase (TIMPs) proteins in transitional cell carcinoma (TCC) cell lines and surgical specimens of the bladder neoplasm. The expression level was correlated to the degree of cellular differentiation and invasiveness of bladder cancer. Panels of six TCC cell lines with different degrees of differentiation were tested with monoclonal antibodies (mAbs) to MMP-1, MMP-2, MMP-3, MMP-9a, MMP-9b, TIMP-1 and TIMP-2 by immunocytochemistry. Gelatin zymography was also conducted on the cell lines for MMP-2 and -9. In addition, immunohistochemistry with the mAbs to MMP and TIM molecules was performed on 30 TCC specimens. We found that TCC cell lines were stained positively for MMP-1 (6/6), weakly for MMP-9a (2/6), MMP9b (5/6) and TIMP-1 (3/6), and negatively for MMP-2 (3/6) and MMP-3 (3/6). Zymographic analysis of the cell lines showed a high level of MMP2 in the MGH-U4 cell line. In bladder cancer surgical specimens, all specimens were positive for MMP1 (30/30), 19 were positive for MMP-2 (63.3%), 21 positive for MMP-9a (70%) and 15 positive for MMP-9b (50%). The expression of MMP-2 was found to be positively correlated with higher-grade tumors (p=0.036) and the expression of MMP-9a and -9b was found to be positively correlated with tumor stage (p=0.012 and 0.023, respectively). However, the expression of MMP-1, MMP-3, TIMP-1 and TIMP-2 was not correlated with either tumor staging or grading. In conclusion, the expression of MMP-2 and -9 was correlated with high-grade or high-stage bladder tumors, respectively. However, this correlation was not observed with TCC cell lines in which high- and low-grade tumors are included. Immunohistochemical results on tumor lesions may have more clinical relevance, since in a given tumor microenvironment the interaction among tumor cells in situ and tumor-associated cells, such as neutrophils, macrophages, lymphocytes and endothelial cells, as well as environmental factors (hypoxia and pH), cytokines and growth factors released by these cells may be required for TCC to express selective MMPs and TIMPs. The selective expression of these molecules then regulates tumor progression.