OBJECTIVE The purpose of this study is to examine the changes of blood-aqueous barrier function in cases of central or branch retinal vein occlusion. METHODS In addition to fluorophotometry of the aqueous humor and posterior vitreous, the authors used a method that quantifies protein in the aqueous (aqueous flare) by measuring the intensity of scattered laser light. RESULTS Aqueous and posterior vitreous fluorescein concentrations and aqueous flare were significantly higher than in unaffected fellow eyes or eyes of visually normal age-matched controls both in central and branch retinal vein occlusions. They also were significantly higher in eyes with central vein occlusion than in those with branch vein occlusion. Among those eyes with central vein occlusion, aqueous and posterior vitreous fluorescein concentrations and aqueous flare were significantly higher in the hemorrhagic than in the venous stasis type of disease. Among eyes with branch vein occlusion, cases at the acute stage showed significantly higher amounts of aqueous and posterior vitreous fluorescein concentrations and aqueous flare than did those with chronic occlusion. CONCLUSIONS The authors believe that increased amounts mainly reflect blood-ocular barrier disruption. Not only the blood-retinal barrier but also the blood-aqueous barrier disruption is a common sequela in the disorder.