We have used a fluorescence-activated cell sorter to study the lymphocyte subpopulations in the intraocular fluids and peripheral blood of 27 patients with uveitis. T lymphocytes predominated in intraocular fluids. A wide variation in the ratio of Leu 3a-positive (helper) cells to Leu 2a-positive (suppressor) cells was found. No correlation was seen between the specific lymphocyte subpopulations and the clinical uveitis activity or steroid treatment. A statistically significant correlation was found between T-cell subsets present in aqueous humor and peripheral blood. Many lymphocytes seem to be present in intraocular fluids secondary to a breakdown of the blood-ocular barrier.