Membrane-type matrix metalloproteinase 1 (MT1-MMP) is a member of the recently identified unique membrane-type subgroup in the matrix metalloproteinase (MMP) family. MT1-MMP has proteolytic activity against components in the extracellular matrix and activates progelatinase A (72-kDa type IV procollagenase/proMMP-2) on the cell surface. Because MT1-MMP is frequently expressed in a variety of tumors, we examined its contribution to their metastatic potential. The mouse lung carcinoma cell line Madison 109 was transiently transfected with a MT1-MMP expression plasmid and inoculated into the tail vein of BALB/c mouse. Fate of the transfected cells was monitored by the neo(r) gene in the plasmid using the quantitative PCR method. The survival rate of the parental cells in lung was 0.7% of the inoculated cells. It was increased by 3-fold with the MT1-MMP transfected cells and the number of the lung nodules increased accordingly. Immunostaining of the consecutive tissue sections revealed that lung nodules expressing MT1-MMP were positive for gelatinase A as well, whereas MT1-MMP-negative cells were not stained for gelatinase A at all. Thus, MT1-MMP-expressing cells acquire specific ability to bind exogenous progelatinase A.