Androgens and estrogens have been implicated in the activation of a variety of sexually-dimorphic, hormone-dependent behaviors in the adult zebra finch. In the present report, several biochemical characteristics of two putative sex steroid receptors, androgen- and estrogen-binding activities, were determined by DNA-cellulose chromatography in brain tissues from these birds. High-affinity, limited-capacity receptors for androgens and estrogens were found in cytosolic extracts of telencephalon, diencephalon-mesencephalon, and metencephalon-myelencephalon from adult male and female zebra finches. Androgen-binding activity reproducibly adhered to DNA-cellulose and was eluted within the 110-150 mM NaCl region of a linear salt concentration gradient. Estrogen receptors adhered to DNA-cellulose and exhibited elution maxima between 170 mM and 210 mM NaCl. Collectively these data indicate that brain regions of zebra finches contain steroid receptors that are similar to those found in the brains of other vertebrates and that their biochemical properties are similar in males and females. Quantitatively, males consistently exhibited higher androgen binding than females in both anterior and posterior telencephalic areas. Females treated with estradiol immediately after hatching exhibited adult levels of androgen binding corresponding to those detected in males. Masculinization of the androgen receptor system by early steroid exposure is discussed.