I131 is accumulated by rabbit ciliary body-iris preparations in vitro and transported out of the living rabbit eye. The secretory system resembles the accumulation of iodide by the thiouracil-treated thyroid gland. It is saturated by iodide and inhibited by perchlorate, thiocyanate and fluoroborate. The mechanism for iodide transport out of the rabbit eye appears to be independent of the analogous transport of iodopyracet and related organic anions.