Objectives. To elucidate the role of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs) in human urothelial cancers, we studied gene expressions of MMPs, TIMPs, and membrane-type 1 matrix metalloproteinase (MT1-MMP) in noninvasive or invasive tumor lines transplanted in mice with severe combined immunodeficiency (SCID). Methods. The UCT-1 tumor line, derived from bladder cancer, is a noninvasive transplantable tumor with no evidence of metastasis. The UCT-2 tumor line, derived from a renal pelvic tumor, extensively invades without metastasis. We examined gene expressions of MMPs-1, 2, 3, 7, 8, 9, 10, and 11, TIMPs-1, 2, and 3, and MT1-MMP in UCT-1 and 2 by semiquantitative polymerase chain reaction analysis. Results. Significantly higher gene expression of MMP-2 was detected in the invasive UCT-2 tumor line than in the noninvasive UCT-1 tumor line. Although both tumor lines expressed TIMP-1 and MT1-MMP, stronger gene expression of MT1-MMP was observed in the UCT-2 tumor line than in the UCT-1 tumor line. The other MMPs or TIMPs were not detected in either of the lines. Conclusions. MMP-2 and MT1-MMP may have an important role in the invasion mechanism of urothelial cancers. (C) 1998, Elsevier Science Inc. All rights reserved.