In four series, each containing five pigmented rabbits, the therapeutic effects of different anti-inflammatory agents on the laser-induced disruption of the blood aqueous barrier was investigated. Utilizing an argon laser, the peripheral iris of the left eye of each animal was coagulated with a total energy input of 1,000 mJ. The right eyes served as controls. After the coagulation the intraocular pressure was monitored at intervals of 10 min, and the anterior chamber was tapped for analysis of the aqueous humour 100 min after treatment. In a fifth group of five rabbits, aqueous humour was analysed without laser or drug treatment. The protein concentration and the activity of the lactate dehydrogenase were analysed in all samples of aqueous humour. A significant effect on the protection of the blood aqueous barrier could be identified in the eyes pre-treated with indomethacin (2 mg/kg body weight, injected intramuscularly), and in those pre-treated with dexamethasone (12.8 mg/kg body weight, injected intravenously; P less than 0.025%). Pre-treatment with aspirin (20 mg/kg body weight, injected intravenously) also had a protective response in the eyes treated by laser. The significance of the results of clinical treatment is outlined.