We have used quantitative zymography to measure levels of the type IV collagenases matrix metalloproteinase (MMP)-9 and MMP-2 in 42 biopsies of transitional cell carcinoma and in 7 biopsies of normal bladder. Mean levels of MMP-9 were significantly higher in tumor compared with normal samples (P = 0.08). Levels of MMP-9 and active MMP-2 increased with tumor grade (test for trend, P = 0.002 and P = 0.05, respectively). Levels of MMP-9 and activated MMP-2 were also higher in invasive tumors than in superficial ones (P = 0.001 and P = 0.008, respectively). In situ hybridization studies showed that the mRNAs for both MMP-2 and MMP-9 were located chiefly in the stroma rather than epithelial tumor cells and were concentrated at the interface between the two tissues.