The concentrations of fibronectin in aqueous humor, measured by ELISA which was developed to detect fibronectin, ranged from 5 ng/ml to 100 ng/ml. Aqueous humor was aspirated from human eyes with cataracts and glaucomas using a 26 gauge needle through the peripheral cornea before making the limbal incision into the anterior chamber during surgery. The results of the study show that the average concentration and standard deviation of fibronectin was 0.136 ± 0.192 microgram/ml in cataract eyes, and 0.962 ± 0.918 microgram/ml in glaucoma eyes respectively. There was a statistically significant difference between both groups (p = 0.000). However, no significant differences according to age and sex were noted. There was no influence due to preoperative intravenous mannitol injection on fibronectin concentration. The source of aqueous fibronectin is still not clearly known and the mechanism of the higher concentration of fibronectin in glaucoma has not been clearly disclosed, however it is thought that normally present fibronectin is accumulated in the anterior chamber because it can not pass the aqueous outflow pathway, or that fibronectin production may be increased in glaucoma.