In man, a temporal relationship exists between rising plasma adrenal androgen concentrations and skeletal maturation. To restudy and extend the in vitro work of Puche & Romano & Howard, we assessed the direct growth-promoting potential of dehydroepiandrosterone (DHA), its sulfate (DHAS), testosterone (T) and dihydroT (DHT) upon hindleg rudiments of chick embryos and newborn mice grown in organ culture. Our experiments utilized chemically defined and variously enriched media; contralateral limbs in medium alone were controls for those incubated with added steroid. Growth was measured by: wet weight, protein content, alkaline phosphatase activity (AP) and 3H-thymidine incorporation. Added steroid did not accelerate growth of tibiae and femora from 11 and 12-day-old chick embryos cultured for up to 7 days. Pulse-labeling experiments and those using chick frontal bones were also negative. In 4-day-old mice only DHA promoted increased protein content (33.7±0.84 {SE} vs 30.2±3.33 μg/mg, p<0.05) and AP (43.3±3.47 vs 35.6±3.85 μg/mg, p<0.05). In 2-day-old mice DHT increased AP (54.5±7.01 vs 45.3±6.35 μg/mg, p<0.05). Conclusions: (1) No direct effect of added adrenal or gonadal steroid on in vitro growth of avian bone rudiments was demonstrable; (2) in a mammal model, only minimal DHA and DHT effects were demonstrable; (3) thus, androgen-stimulated bone maturation in man may relate to late development of androgen receptors or depend upon in vivo intermediary growth factors.