Vitreous fluorophotometry performed on 22 patients with moderate to severe hypertension showed that patients with active retinopathy, as manifested by retinal hemorrhages, cotton-wool spots, retinal exudates and edema, or disc edema, generally had elevated values (20/28 eyes). Control of the BP resulted in a decrease in the values toward the normal range. Patients with only arteriolar sclerosis, even some with particularly high BP, generally had normal fluorophotometric values (14/16 eyes). The two exceptions showed minimal elevations. Vitreous fluorophotometry is a useful tool to quantitate the blood-retinal barrier in patients with moderate to severe hypertension and may be a sensitive indicator of treatment efficacy.