·AIM:To evaluate the expressions of nitric oxide(NO)and VEGF in vitreous humor and blood samples in patients with proliferative diabetic retinopathy(PDR)and in patients with branch retinal vein occlusion(BRVO)and to compare the levels with those of controls.·METHODS:NO concentrations were determined using the Greiss reaction in plasma and vitreous humor sam-ples.VEGF levels were assayed by ELISA.The patients in the studies were divided into four groups:16 patients with PDR,5 patients with BRVO,11 patients with rhegmato-genous retinal detachment and 10 patients with macular hole.·RESULTS:The vitreous fluid levels of NO were signifi-cantly higher in patients with PDR than those in other three groups(15.2,4.6-50.9μmol/L,all P<0.01).The con-centration of VEGF were significantly higher in patients with PDR and BRVO than other two groups(P=0.0008,1507.2,50.7-3722.0mg/L;838.8,212.7-850.6mg/L respec-tively),but highest in PDR(P=0.001).There was no significance with NO and VEGF in serum in four groups.There was no correlation with that of NO and VEGF in four groups whatever in vitreous or plasma.·CONCLUSION:The results suggest that higher levels of NO and VEGF may be related to the angiogenesis in DR.·