Using a tritium-sensitive film and [3H]-clonidine, alpha 2-adrenergic receptors were localized in entire eye sections of rabbits and rats. This radioactive agonist specifically labelled three structures in albino animals: ocular muscles, ciliary processes and retina. In pigmented animals, uvea with melanin was intensively but nonspecifically labelled. Microscopic analysis of autoradiograms obtained with iris-ciliary bodies, revealed that the major localization of binding sites was in the ciliary process epithelium. In displacement studies, [3H]-clonidine binding was inhibited by alpha 2-adrenergic compounds while alpha 1- or beta-selective drugs had no inhibitory effects.