A short term incubation of baboon fetal adrenal cells obtained at midgestation and near term was used to determine whether a change in the regulation of androgen formation occurs with advancing gestation. Adrenal glands were removed from baboon (Papio anubis) fetuses on day 100 (mid; n = 7) or day 170 (late; n = 5) of gestation, and cells were dispersed with 0.2% collagenase. Cells (10(5] were incubated at 37 C for 3 h in medium 199 in the presence or absence of 10 nM ACTH, 10 nM ovine PRL, 10 nM ovine GH, 50 nM hCG, or 50 nM human chorionic somatomammotropin. Dehydroepiandrosterone (DHA), DHA sulfate (DHAS), cortisol (F), and androstenedione concentrations were determined in the medium by RIA. At midgestation, ACTH, PRL, and GH elevated (P less than 0.05) DHA (168%, 169%, and 178%, respectively) and DHAS (142%, 210%, and 197%, respectively) formation. Near term, ACTH and PRL retained their ability to stimulate (P less than 0.05) DHA (307% and 220%, respectively), but not DHAS, synthesis. The fetal adrenal at late gestation, however, lost its ability to respond to treatment with GH. hCG and human chorionic somatomammotropin did not stimulate steroidogenesis at either time of gestation. F formation at midgestation was less (P less than 0.05) than that at term and not responsive to ACTH. ACTH stimulated (P less than 0.05) F secretion by 68% in fetal adrenal cells obtained near term. The secretion of androstenedione was not affected by any peptide treatment at either stage of gestation. These data indicate that the responsivity of the baboon fetal adrenal to various pituitary peptides is different at two developmentally distinct stages of gestation. We conclude, therefore, that the regulation of fetal adrenal steroidogenesis changes with advancing gestation.