We evaluated the efficacy of N-Acetyl-Aspartyl-Glutamic acid (magnesium salt) (NAAGA) eye-drops in preventing the conjunctival and uveal allergic inflammation induced by reverse passive Arthus reaction in the rabbit. The permeability of the blood-conjunctival and blood-aqueous barriers was investigated by the leakage of125I-labelled rabbit serum albumin injected intravenously prior to the challenge with the antigen. Permeability of both barriers was markedly increased 2 hours after the triggering of the allergic reaction; marked edema of the conjunctiva was also observed. Pretreatment with 1, 3,6% (w/w) NAAGA eye-drops prevented the conjunctival inflammatory changes in a dose related manner and to a lesser degree, the breakdown of the blood-aqueous barrier. The distribution of topically applied14C-NAAGA in the rabbit eyes was also investigated.