To investigate the levels of endothelin-1 (ET-1), homocysteine (Hcy), vitamins A, E, B12 and folic acid in plasma of patients with different types of glaucoma: primary open-angle glaucoma (POAG) and normotensive glaucoma (NTG). Patients were classified into 3 groups: group POAG comprised 48 patients, group NTG comprised 15 patients, and control group that comprised 75 healthy subjects. ET-1 levels were measured by ELISA, Vitamins A and E by HPLC, and Vitamin B12, homocysteine, and folic acid levels were determined by chemiluminescent immunoassay. The ET-1 and Hcy levels were significantly higher (p = 0.002) in the POAG group compared to NTG and control group. Vitamin E levels were significantly lower (p = 0.001) in the NTG group compared to POAG and control group. The increase of Hcy and ET-1 in POAG patients is related to vascular endothelial dysfunction. Thus results may play a key role in the development of this disease. Lower levels of Vitamin E in the NTG group suggest that oxidative process plays an early role in the development of this type of glaucoma.