Beta-blockers are widely used in the primary open angle glaucoma treatment. The molecular mechanism by which these drugs reduce intraocular pressure is essentially based on the blockade of beta-adrenergic receptors localized on the ciliary processes. Vascular effects of beta-blockers, which are difficult to exhibit clinically, have been recently reported for some drugs with intrinsic sympathomimetic activity. In this study, we attempted to investigate the presence of beta-adrenergic specific binding sites on the human retinal vessels, by means of an in vitro autoradiographic technique. These receptors are localized both on arteries and veins; displacement studies indicated that they are mainly of beta-2 subtype.