Activated gelatinase A is reportedly associated with tumor spread. We identified novel matrix metalloproteinases that localize on the cell surface and mediate the activation of progelatinase A. Thus, these progelatinase A activators were named membrane-type matrix metalloproteinase-1 and −2 (MT-MMP-1 and −2, respectively). MT-MMP-1 is overexpressed in malignant tumor tissues, including lung and stomach carcinomas that contain activated gelatinase A. This suggests that MT-MMP-1 is associated with the activation of progelatinase A in these tumor tissues. The expression of MT-MMP-1 also induced binding of gelatinase A to the cell surface by functioning as a receptor. The cell surface localization of proteinases has advantages over pericellular proteolysis. MT-MMP -1 and its family may play a central role in the cell surface localization and activation of progelatinase A and via this mechanism, tumor cell use exogenous progelatinase A to mediate the proteolysis associated with invasion and metastasis.