Background: Cytokine levels are elevated in the ocular fluid of diabetic patients. It is unclear whether aqueous humor levels of vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6) are related to the vitreous fluid levels of these substances and to the progression of diabetic retinopathy. Methods: Aqueous humor and vitreous fluid samples were obtained during cataract and vitreous surgery from ten eyes of ten patients with diabetic macular edema and 26 eyes of 26 patients with proliferative diabetic retinopathy (PDR). The VEGF and IL-6 levels in aqueous humor, vitreous fluid, and plasma were measured by enzyme-linked immunosorbent assay. Results: VEGF and IL-6 levels in aqueous humor were significantly correlated with those in vitreous fluid (P=0.793 and P=0.737, respectively). VEGF levels in aqueous humor and vitreous fluid were signifi cantly correlated with the corresponding IL-6 levels (P=0.631 and P=0.687, respectively). The aqueous and vitreous levels of VEGF were significantly correlatedwith the severity of diabetic retinopathy (P=0.659 and P=0.771, respectively). Aqueous and vitreous levels of IL-6 were also significantly correlated with the severity of diabetic retinopathy (P=0.742 and P=0.746, respectively). Aqueous and vitreous levels of both VEGF and IL-6 were significantly higher in the patients with active PDR than those in quiescent PDR. Conclusions: Our results suggest that there is a significant relationship between VEGF and IL-6 levels in aqueous humor and in vitreous fluid. Measurement of the aqueous levels of VEGF and IL-6 may be useful to analyze the pathogenesis of diabetic retinopathy and to predict disease activity. Background: Cytokine levels are elevated in the ocular fluid of diabetic patients. It is unclear whether aqueous humor levels of vascular endothelial growth factor (VEGF) and interleukin-6 (IL-6) are related to the vitreous fluid levels of these substances and to the progression of diabetic retinopathy. Methods: Aqueous humor and vitreous fluid samples were obtained during cataract and vitreous surgery from ten eyes of ten patients with diabetic macular edema and 26 eyes of 26 patients with proliferative diabetic retinopathy (PDR). The VEGF and IL- 6 levels in aqueous humor, vitreous fluid, and plasma were measured by enzyme-linked immunosorbent assay. Results: VEGF and IL-6 levels in aqueous humor were significantly correlated with those in vitreous fluid (P = 0.793 and P = 0.737, respectively) . VEGF levels in aqueous humor and vitreous fluid were signifi cantly correlated with the corresponding IL-6 levels (P = 0.631 and P = 0.687, respectively). The aqueous and vitreous levels of VEGF were Aqueous and vitreous levels of IL-6 were also significantly correlated with the severity of diabetic retinopathy (P = 0.742 and P = 0.746, respectively). Aqueous and vitreous levels of IL-6 were also significantly correlated with the severity of diabetic retinopathy (P = 0.659 and P = and vitreous levels of both VEGF and IL-6 were significantly higher in the patients with active PDR than those in quiescent PDR. Conclusions: Our results suggest there is a significant relationship between VEGF and IL-6 levels in aqueous humor and in vitreous fluid . Measurement of the aqueous levels of VEGF and IL-6 may be useful to analyze the pathogenesis of diabetic retinopathy and to predict disease activity.