Fibrinogen concentration in the aqueous humor of buphthalmic rabbits, AXBU/J, and those of the normal parent strain AX/J are 0.36±0.14 and 0.08±0.01 mg/ml, respectively. There was no detectable fibrinogen in the aqueous humor of normal inbred strain III/J rabbits. Among the buphthalmic rabbits, elevated fibrinogen concentration in the aqueous humor was observed in two month old prodromal rabbits, indicating a small leakage of fibrinogen into the anterior chamber before the development of buphthalmia. Protein concentration in the aqueous humor was close to normal, in spite of an elevated level of fibrinogen in the young buphthalmic rabbits. Severe protein leakage was seen in only some of the old buphthalmic rabbits.