By light and electron microscope radioautographyin vivo, competitive binding sites for125I-Arg 101-Tyr 126 atrial natriuretic factor were localized mostly on the“pigmented”epithelium of the rat ciliary process. Further investigation using isolated ciliary processes from rabbits demonstrated the presence of specific receptors for125I-atrial natriuretic factor. In addition, synthetic atrial natriuretic factor inhibited basal and stimulated adenylate cyclase activity.These results demonstrate for the first time the presence of specific receptors for atrial natriuretic factor in the ciliary processes which are negatively coupled to adenylate cyclase. The possible role of this peptide in the control of intraocular pressure is suggested.