PURPOSE To evaluate the relationship between vascular endothelial growth factor (VEGF) and extracellular superoxide dismutase (EC-SOD) in vitreous body and serum in patients with proliferative diabetic retinopathy (PDR), and investigate the role of EC-SOD in PDR by evaluating its angiostatic effect, using an in vitro angiogenesis model. To investigate the role of EC-SOD in PDR by evaluating its angiostatic effect, using an in vitro angiogenesis model. METHODS EC-SOD and VEGF concentrations in vitreous and serum samples from PDR and macular hole (MH) were measured by ELISA. The effects of EC-SOD on VEGF-induced proliferation, migration, and tube formation were evaluated using human umbilical vein endothelial cells (HUVECs). Moreover, the effects of EC-SOD on VEGF-induced proliferation and migration were evaluated in HUVECs and primary normal human retinal microvascular endothelial cells. RESULTS Intravitreal concentrations of EC-SOD were significantly higher (p<0.01) in PDR (58.0+/-23.8 ng/ml, mean+/-SD) than in MH (29.3+/-6.6 ng/ml). Intravitreal concentrations of VEGF were dramatically higher (p<0.01) in PDR (798.2+/-882.7 pg/ml) than in MH (17.7+/-15.5 pg/ml). The serum concentrations of EC-SOD and VEGF did not differ between the two patient groups. The vitreous concentrations of VEGF correlated with those of EC-SOD in all patients (rs=0.61, p<0.001). In HUVECs, EC-SOD at 100 ng/ml significantly suppressed VEGF-induced proliferation and tube formation, but not VEGF-induced migration. CONCLUSIONS EC-SOD was increased together with VEGF in the vitreous body from PDR patients, suggesting that EC-SOD may play a pivotal role in the pathogenesis of angiogenesis.