To investigate the factors related to lymph node metastasis of testicular germ cell tumors, we first established a seminoma orthotopic model with lymph node metastasis in SCID mice by inoculating small fragments from subcutaneous xenografts. Second, we compared the expression patterns of metastasis-related genes of the seminoma xenografts and of the TCam-2 cells which were established as a seminoma cell line from a primary testicular seminoma. Third, we immunohistochemically analyzed human germ cell tumors (25 seminomas, 17 nonseminomas) using monoclonal antibodies to CD34, VEGF, VEGF-C, Flt-4, MMP-2 and E-cadherin. Testicular seminoma xenografts grew in 32/32 (100%) of the inoculated mice, of which 15 (47%) developed macroscopic metastasis to the renal hilar lymph node. Circulating tumor cells were detectable by using a PCR assay for the human beta-globin gene in 25/32 (78%) mice, although metastatic foci were not histologically evident in the visceral organs, including lungs, liver, kidneys and spleen. This may reflect the lymphophilic characteristics of the seminoma cells used. Regarding mRNA expression of metastasis-related genes, an increased expression of MMP-2 and VEGF compared with that in the s.c. xenografts was demonstrated by RT-PCR assay in the testicular seminoma xenografts. In addition, uPAR, MMP-1, MMP-2, MT1-MMP and MT3-MMP showed a a stronger expression and PAI-2 a weaker expression in the seminoma xenografts than did TCam-2 cells. These results suggest a higher metastatic potential of the seminoma xenografts, especially testicular xenografts, as compared with TCam-2 cells. In the immunohistochemical study, a significant correlation was found between MMP-2 expression and lymph node metastasis, which is compatible with the results for the metastasis-related gene expression from the seminoma xenografts.