Most estrogen actions are mediated by two estrogen receptor subtypes (ERalpha and ERbeta). While a single ERbeta appears to be present in higher vertebrates, two forms of ERbeta encoded by different genes have recently been isolated in some teleost fish species. We investigated whether this also applies to the hermaphrodite sparid sea bream (Sparus auratus) and cloned a second ERbeta (sbERbeta2) in this species. We have also compared the tissue distribution of the three receptors as yet identified in sea bream, designated sbERalpha, sbERbeta1, and sbERbeta2.