We prospectively evaluated the adverse reactions of apraclonidine in 20 normal volunteers by instilling a single drop of 1% apraclonidine in their right eyes. Examinations, including blood pressure, pulse rate, conjunctiva and cornea, intraocular pressure (IOP), pupil diameter, basal tear secretion and margin reflex distance of both upper and lower eyelids, were performed prior to entry and at 1, 3, 5 and 7 hours after instillation. The ocular hypotensive effects were statistically significant for apraclonidine-treated eyes throughout the study and also statistically significant for contralateral eyes from three hours after topical administration of 1% apraclonidine. Decreases in systolic blood pressure were statistically, but not clinically, significant. No significant changes in diastolic blood pressure, pulse rate and basal tear secretion were noted. Conjunctival blanching and mydriasis were commonly found. Upper lid retraction was frequently noted. While the elevations of the upper lid margin in most subjects were not more than 2 mm and did not cause noticeable change in appearance, one subject suffered from mechanical entropion and marked corneal abrasion 3 hours after instillation of the medication. This may well be a particularly notable finding in Asian people.