There is increasing evidence that 17beta-estradiol is necessary for normal male fertility. The aim of the present study was to characterize estrogen receptor beta (ERbeta) expression in a non-mammalian vertebrate model, the lizard (Podarcis s. sicula) testis. Immunocytochemical analysis shows that ERbeta proteins are present among germ cells in the nucleus of the spermatogonia, in primary spermatocytes and spermatids. Western blot analysis with antibodies against the ERbeta gene product revealed an isoform with a specific weight of 55 kDa. In conclusion, the widespread expression of ERbeta in the Podarcis s. sicula testis is consistent with a role for estrogens in modulating spermatogenesis in the male.