Two DM-domain genes, DMY (sex-determining gene) and DMRT1, have been reported to be expressed in the testis of medaka. In this study, a specific RT-PCR assay was used to determine the expression patterns of DMY and DMRT1 in various tissues of medaka during different stages of development. The results show that the transcripts of both DMY and DMRT1 are present not only in testes but also in several other tissues from fry and adults of medaka.