The effect of electrical stimulation of the sympathetic nerves on the blood-aqueous barrier was investigated in rabbits. The permeability of the barrier was assessed during either acute, chronic or following chronic nerve stimulation. During acute and chronic stimulation of the sympathetic nerves, fluorescein entered the anterior chamber at a rate significantly slower than in control eyes. After chronic stimulation, both the rate of entry of fluorescein and the aqueous humor protein concentration were much greater than in control eyes indicating breakdown of the blood-aqueous barrier. Treatment with the non-steroidal anti-inflammatory drugs, indomethacin and suprofen, completely blocked the breakdown of the blood-aqueous barrier. These results indicate that sympathetic nerve stimulation can cause the local synthesis of prostaglandins and that these can affect the blood-aqueous barrier.