To determine whether inflammatory cytokines are increased in proliferative diabetic retinopathy. We measured concentrations of interleukin-6, 8 (IL-6, 8) and tumor necrosis factor (TNF)-alpha by enzyme-linked immunosorbent assay (ELISA) in vitreous and serum from 47 patients with proliferative diabetic retinopathy and 21 patients with vitreous noninflammatory retinopathies. Vitreous concentration of IL-6 were 64.7+/-12.8 pg/ml in proliferative diabetic retinopathy, much greater (P<.005) than in noninflammatory retinopathy (2.8+/-4.5 pg/ml). Amounts of IL-8 in vitreous fluid also were greater in proliferative retinopathy than in noninflammatory retinopathy (34.0+/-11.5 vs. 6.1+/-2.0 pg/ml, P<.005). Concentrations of TNF-alpha in vitreous fluid were not statistically different in proliferative retinopathy from those in noninflammatory retinopathy. In sera, concentrations of IL-6 and IL-8 were not different between proliferative and noninflammatory retinopathy. However, serum TNF-alpha was much greater in proliferative retinopathy than in noninflammatory retinopathy (0.81+/-0.72 vs. 0.09+/-0.00 pg/ml, P<.001). Elevated TNF-alpha in serum then may be diagnostically useful in proliferative diabetic retinopathy. And inflammatory cytokines in vitreous may be pathogenically important in this concentration.