Aminopeptidase N/CD13 is a Zn(2+)-dependent exoprotease present on the cell surface as a transmembrane protein. Our previous studies using aminopeptidase inhibitors and antibodies demonstrated that aminopeptidase N is involved in the degradation and invasion of the extracellular matrix (ECM) by metastatic tumor cells. In the present study we transfected human A375M melanoma cells with eukaryotic plasmid expression vectors that contained full length cDNA of aminopeptidase N/CD13 and examined their characteristics. The transfectants that expressed extremely high levels of aminopeptidase N/CD13 degraded type IV collagen and invaded ECM more actively than the parental and control vector-transfected cells. Furthermore, the aminopeptidase N/CD13-transfected A375M cells had significantly augmented lung colonizing potential in nude mice. The results show that the aminopeptidase N/CD13 plays an active role in degradation and invasion of ECM and may be involved in the molecular mechanisms of blood-borne metastasis.