Aqueous humor from human glaucomatous eyes was divided into two groups. Group I aqueous humor contains a negligible amount of ascorbate, while group II contains ascorbate. Group I aqueous humor stimulates ascorbate oxidation. This oxidative effect is inhibited by the addition of EDTA, indicating the presence of metallic ions. The amount of copper determined by atomic spectro-photometry in these samples was 1.54μg/ml. On the contrary, group II aqueous humor protects against ascorbate oxidation. The small amount of albumin present in these samples accounts for part of this protective effect.