Studies were performed to elucidate the ontogeny of a single class of androgen binding protein in male rat liver cytosol which exhibits characteristics of a ligand specific, high affinity (Kd = 2.3 nM), 8S-receptor capable of nuclear translocation. Detectable levels of receptor first appear at 45 days of age in the male and reach maximum concentration at 65 days. Barely detectable levels are seen in females throughout the duration of study (80 days). Gonadectomy in both sexes (65 days) and androgen treatment of oophorectomized females do not alter the normal development of sexual differentiation of the high affinity androgen receptor. After neonatal castration (2 days) and DES replacement however, receptor sites do not undergo differentiation and adult males exhibit female levels. Conversely, neonatal androgen replacement in 2-day castrates partially restores the level of binding sites to control males values (TP, 71%; DHT, 51%). Neonatal castration without replacement retards but does not fully eliminate sexual differentiation of levels of receptor sites in adult males. Likewise, neonatal androgen treatment in females results in a partial masculinization of binding sites. Following hypophysectomy, levels of receptor sites in females are similar to intact or hypophysectomized males; sexual differences in the adult are abolished. These studies suggest that sexual differentiation of specific liver cytosol androgen binding sites in the adult may be partially programmed at birth by testicular androgen and furthermore, adult sexual dimorphism is maintained through an inhibitory influence of the pituitary in the female.