Computerized anterior-chamber fluorophotometry was used to investigate the effect of unilateral antiglaucomatous trabeculectomy on the dynamics of aqueous humor in the unoperated fellow eye. In 14 patients with bilateral primary open-angle glaucoma, pigmentary glaucoma or exfoliation glaucoma, antiglaucomatous trabeculectomy was performed in one eye in which medical management of glaucoma had failed. The fellow eye in all patients had a well-defined history of glaucoma and had been treated with different sorts of medication. The medical management of the unoperated fellow eyes was continued throughout the study. Aqueous humor flow was measured in these eyes prior to surgery and on the 5th day after trabeculectomy. Systemic medication was discontinued from 48 h prior to surgery until second fluorophotometry. The average postoperative flow in the fellow eyes increased from 2.56 to 2.92 microliters/min (P less than 0.05%, paired t-test). The increase in flow in the fellow eyes was independent of topical antiglaucoma medication and of the diurnal rhythm of aqueous humor dynamics. The results of the study indicate that filtration surgery in one eye triggers a CNS-mediated, reflective increase in aqueous flow to maintain physiological stability in the anterior chamber of the surgically treated eye. Since this CNS reflex on aqueous humor dynamics affects both eyes, the clinical observation of intraocular pressure (IOP) dysregulation in the unoperated fellow eye following unilateral trabeculectomy is now understandable.