Adrenomedullin (AM), a novel hypotensive peptide, is suggested to be involved in defense mechanisms against hypertension, however, the detail mechanisms have not been clarified. To elucidate whether AM synthesis would be altered in a salt dependent hypertension, we have investigated the AM concentration and AM messenger RNA (mRNA) level in tissues of Dahl salt-sensitive rats on either low- or high-salt intake. The AM concentration in cardiac ventricle of the high-salt group was significantly higher than that of the low-salt group. The plasma AM concentration was also significantly higher in the high-salt group than in the low-salt group. Furthermore, the plasma AM concentration correlated well with the weight of left ventricle. RNA blot analysis revealed that the AM mRNA level in cardiac ventricle of the high-salt group was higher than that of the low-salt group. These results suggest that AM participates in the pathophysiology of salt dependent hypertension and plays a role in cardiac hypertrophy.