Melanoma antigen (MAGE), a tumor-associated antigen, is a product of members of a gene family that consist of 24 structurally related genes. MAGE genes are expressed only in the testis among normal tissues, but they are also expressed in a number of human tumors of various histological types. Although the MAGE expression is primarily regulated by the genome-wide demethylation of CpG dinucleotides, the demethylation of CpG dinucleotides does not always result in the MAGE expression. In the present study, we demonstrated that 40 mM NaCl induces the transcriptional and translational activation of MAGE-B1 and -B2 in specific tissues. The mRNA stability analyses revealed that the half-life of the MAGE-B1 mRNA is about 5 h. No change in the stability of the MAGE-B1 mRNA was induced by the NaCl treatment, which suggests the transcriptional activation of MAGE-B1 by NaCl. This is the first report that the MAGE expression is regulated by means other than the genome-wide demethylation of CpG dinucleotides.