Saturation analysis over a wide range of [3H]estradiol-17 beta concentrations (1-40 nM) in cytosols prepared from liver of the newt Pleurodeles waltl of both sexes revealed a sex-linked heterogeneity of the estradiol-17 beta binding sites. In females, one type of binding site has been identified as a classical receptor. It exhibited a high affinity for estradiol-17 beta (Kd = 9 X 10(-9) M), had a high specificity for estrogenic compounds and was stabilized by monothioglycerol. In males, in addition to the receptor found in females, a second estrogen binding component was detected, not observed in female cytosols. It exhibited a Kd of 4.8 X 10(-8) M for estradiol 17 beta, higher capacity and displayed the same highly specific estrogen binding as does the estrogen receptor. It was affected by monothioglycerol and its binding was found to be significantly increased on cytosol dilution, as well as by estrogen-treatment.