Despite recent extensive immunohistochemical studies, the expression patterns of CD44 in testicular germ cell tumors are still controversial. In the present study, we investigated the CD44 gene expression in 40 specimens including 18 seminomas, 16 nonseminomatous germ cell tumors (NSGCT), and 6 normal testes by reverse transcriptase-polymerase chain reaction and Western blotting. Reverse transcriptase-polymerase chain reaction analysis revealed that the standard CD44 isoform (CD44s) was expressed in all of the specimens, whereas the variant CD44 isoforms were highly expressed in NSGCTs but barely detectable in seminomas and normal testes. In addition, we confirmed by direct DNA sequence analysis that the predominantly expressed variant isoform in NSGCTs was CD44v8-10. In germ cell tumors, these results were paralleled in Western blot analysis; that is, CD44s protein was expressed in all of the tumor specimens, whereas high molecular weight variant isoforms were expressed only in NSGCTs. However, at the protein level, no detectable CD44 was expressed in normal testes. These findings show that the combined assessment of CD44 expression patterns at both the RNA and protein levels enables us to distinguish among seminoma, NSGCT, and normal testis specimens; hence, it could serve as a useful practical adjunct to conventional diagnostic methods for testicular germ cell tumors.