Excess iodide and the accumulation of 125I by the thyroid, plasma and developing oocytes of the Japanese quail.

1. Developing oocytes of the Japanese quail accumulated 0-44 microgram of each 1 microgram of 125I-labelled iodide after intra-muscular injection of doses up to 500 microgram iodide as NaI but only 0-007 microgram after injection of more than this: the abrupt change in the rate of accumulation was attributed to saturation of the iodide transport mechanism. 2. The proportion of available iodide transferred into the oocytes appeared to be more dependent on the amount of iodide injected and the total weight of growing oocytes than on a requirement for either a store of iodide for the embryo or an iodide excretory pathway for the hen. 3. The thyroid was about four times more active in accumulating iodide than the oocyte. 4. The percentage of iodide accumulated by the plasma was the same at all dose rates.