Acute anterior uveitis in response to the administration of systemic gram-negative endotoxin was studied in humans. The blood-aqueous barrier was evaluated in eight normal human subjects at 8 or 24 hours after systemic administration of purified gram-negative endotoxin. No significant changes in the blood-aqueous barrier were found, as evaluated by permeability to fluorescein, number of aqueous cells, flare, or intraocular pressure, despite profound endotoxin-induced cardiac, pulmonary, and circulatory effects. Gram-negative endotoxin does not appear to affect the human blood-aqueous barrier in doses that can safely be given to humans.