I compared Japanese quail Coturnix japonica, and Ring doves Streptopelia risoria, in the development of thyrotropin (TSH) influence on thyroid hormone (TH) content in the thyroid gland (TG) and the serum, and on TG-cAMP content. In embryos, pituitary gland (PG)-TSH content was measured by an avian bioassay system. Adult quail and doves were studied for comparability of thyroid gland function when receiving comparable dietary iodine. Also, thyroid function in adult doves was compared with different iodine intake. In embryonic quail, there is considerable maturation of thyroid function prior to hatching, TG-TH content is low but detectable in day 8 embryos; TG-TH content increases 300X between day 8 and hatching (16.5 day incubation). Pituitary TSH was detectable on embryonic day 8, with higher levels found closer to hatching. The TG of 8 day embryos responds to TSH injection by increased TG-cAMP content but the serum TH response to TSH does not mature until day 9. Serum TH concentrations suggest that the TG is under the control of endogenous TSH from the pituitary during the latter part of incubation. In doves, most of the development of thyroid function and the maturation of its pituitary control occur after hatching, Thus, thyroid functional development is much later in doves than in quail. TG-TH content is extremely low in embryos and nestlings up to 3 days after hatching, increases slowly innestlings up to day 10, then increases sharply. Serum TH are very low in embryos and rise steadily in nestlings to plateau after day 8. Pituitary TSH content is undetectable in embryos and in nestlings until day 4. The TG does not respond (based on serum TH concentrations) to TSH injection through the day of hatching (day 16; mean incubation period of 16.5 days), but an increase in serum TH occurs in day 2 nestlings in response to TSH injection. The magnitude of this response continues to increase during the first week after hatching. In adult birds, thyroid function was studied in Japanese quail and Ring doves, when both were fed the same dietary iodine (I; 930 μg I/kg). We also compared thyroid function in groups of doves receiving low I (< 100 μg I/kg) or moderate I (930 μg I/kg). We measured thyroid gland (TG) weight, TG stable I (¹²⁷I) I content, TG ¹²⁵I uptake, ¹²⁵I labeling of thyroid hormones, and serum ¹²⁵I thyroxine (T4) half-life. Triiodothyronine (T3) and thyroxine (T4) concentrations in TGs and serum also were determined. Our results indicate that doves and quail receiving the same dietary I show similar serum T3 concentrations and TG functional state, but that there are some differences between the species in the way which this equivalent functional state is achieved. Doves fed low dietary 1 (< 100 μg 1/kg) when compared to doves with moderate I intakes (930 μg I/kg) showed similar serum T3 concentrations despite reduced serum T4 concentrations and TG-hormone stores. This study demonstrates that quail and doves show similar TG function and a similar regulation of serum T3, the · presumed metabolically active hormone, when dietary I availability is the same. Also, doves with low dietary I show decreases in some measures of TG function compared to doves with moderate I, but still maintain a level of serum T3 comparable to that with adequate I intake. This set point regulation of T3 therefore appears to be independent of serum T4 or TG hormone stores. / Ph. D.