The effect of estradiol-17β (E 2) given as a sustained-release implant (Compudose 200) on concentrations of plasma calcium (Ca) and the development of the chick shell gland has been investigated in food-restricted and thyroid hormone-treated 6- to 8-week-old broiler breeder pullets. Chicks implanted with 0, 0.5, 1.0, 1.5, 2.0, and 3.0 Compudose pellets for 24 days ( n = 6/group) revealed a dose-response relationship between plasma E 2 and Ca and on oviduct growth. Plasma E 2 concentrations were characterized by an initial burst phase for approximately 17 days, followed by a constant release phase. Histologic examination of shell gland tissue confirmed the dose related E 2-induced development of microvilliated epithelium and tubular glands over time. Feed restriction initiated at 2 weeks of age markedly increased the response to the E 2 implants. Birds ( n = 8/group) implanted with 2 pellets and feed restricted had increased plasma concentrations of E 2 and Ca, and increased growth of the oviduct ( P < 0.01) as compared to ad libitum implanted birds. In a separate study birds ( n = 6/group) had restricted access to feed from 8 weeks of age and were implanted with 0, 2, 4, or 8 pellets. At intervals from 9 to 45 days after implantation one bird from each group was killed. Although concentrations of plasma Ca were significantly greater in feed-restricted birds ( P < 0.01), oviduct growth was only marginally increased by the food restriction program. Plasma Ca concentrations in broiler breeder pullets ( n = 8/group) implanted with 1 or 3 pellets and injected with T 3 T 4 (100 μg/day) were significantly decreased ( P < 0.05). Injection of thyroid hormone also marginally decreased shell gland epithelial cell height ( P < 0.05) and development of microvilli ( P < 0.05). There was no effect of the administration of the goitrogen, propylthiouracil (10 μg/day im), on the E 2 induced development of the shell gland.