Of all malignancies diagnosed in men between 17 and 45 years of age, 60% are germ cell tumors (GCT). GCT arise from carcinoma in situ cells, which are thought to originate from a transformed fetal germ cell, the gonocyte. Seminoma together with embryonal carcinoma represent the most frequent subtypes of GCT. However, the nature of the molecular pathways involved in seminoma formation remains elusive. Therefore, analysis of appropriate cell culture systems is an important prerequisite for further understanding of the etiology of this tumor entity. Although several cell lines for embryonal carcinoma have been established and analyzed, so far only two cell lines from seminoma patients have been reported. In the present study, we have analyzed these seminoma cell lines (TCam-2 and JKT-1) and compared the gene-expression profiles with those of normal tissue and of seminoma and embryonal carcinoma by using DNA Array technology. We have found that TCam-2 clusters with the group of classical seminoma, whereas JKT-1 clusters with the group of embryonal carcinoma. Using reverse transcription/polymerase chain reaction, Western blot, and immunohistochemistry, we have confirmed the seminoma-like nature of TCam-2, whereas JKT-1 lacks expression for most of the genes detectable in GCTs, thus making doubtful the germ cell nature of this cell line. The data represent the first genome-wide expression analysis of the two cell lines and comparison/clustering with subgroups of germ cell tumors. Only TCam-2 seems to represent a suitable in vitro model for seminoma.