The purpose of this work was to study the role played by the pituitary in the overall estrogenic response of the quail oviduct during the first 30 days of life. The oviduct response (weight, soluble protein, and DNA content) was measured in castrated and castrated-hypophysectomized quails 24 h after a single im dose of 0.1 or 1 mg estradiol benzoate (EB)/kg BW. The effect of ACTH (0.5 mg/kg) and corticosterone (1 mg/kg) alone or in combination with EB has been investigated as well. The monitored parameters show different patterns as a function of age whether the castrated quails were injected with 0.1 mg or 1 mg EB/kg. These patterns are linear in quails treated with low doses of EB and nonlinear in animals treated with high doses of EB. In this latter group, the oviduct responses to EB, regardless of parameter measured, are constant from days 8-18, increase progressively from days 18-22, and are constant again from days 22-30. Hypophysectomy, ACTH administration, or corticosterone administration does not have a significant effect on the growth of the oviduct (weight, soluble protein, and DNA content) of castrated quails and does not modify the oviduct growth and protein accumulation induced by the injection of 0.1 mg EB/kg over the period studied. On the contrary, in quails treated with 1 mg EB/kg, hypophysectomy selectively suppresses the increased estrogenic response of the oviduct seen after day 18. The cumulative results presented indicate that in castratedhypophysectomized quails injected with 1 mg EB/kg, exogenous corticosterone or ACTH administration compensates for the deleterious effect of hypophysectomy. These observations further suggest that the pituitary (via ACTH and corticosterone) has a synergistic effect with estrogen administration on oviduct growth and protein accumulation. The triggering of this pituitary contribution is age dependent. (Endocrinology106: 1392, 1980)