The levels of lipid hydroperoxide (LHPs) in vitreous are elevated in a variety of retinal disorders. Recently, we have shown that increased levels of LHPs in the vitreous enhanced leukocyte-endothelium interaction in the retina, which should contribute to the initial disturbance of the retinal microcirculation. Based upon the previous work, the purpose of the present study was to investigate the effect of polyethylene glycol-superoxide dismutase (PEG-SOD), one of the important enzyme antioxidants, on leukocyte-endothelial interaction in the retinal microcirculation under LHP-induced oxidative stress. Male Brown-Norway rats weighing approximately 250g were used. LHP(18:2) was made from linoleic acid (LA) with lipoxygenase and 10μg of LHP dissolved in 5μl of sodium borate buffer (SBB, 0.02m) was slowly injected into the vitreous using a 33-gauge needle. PEG-SOD (5000units/kg) was given intravenously 5min before LHP injection. At 2, 4, 6, 12, 24 and 48hr after the vitreous injections, we evaluated the number of rolling leukocytes along the major retinal veins and the number of leukocytes that accumulated in the retinal microvasculature with acridine orange digital fluorography. In LHP-treated rats, leukocyte rolling along the major retinal veins was maximal at 6hr after LHP injection. The number of rolling leukocytes in the PEG-SOD-treated rats was decreased to 5.5% of those in the LHP-treated rats at 6hr after LHP injection (P<0.01). No rolling leukocytes were observed in either control or vehicle-treated eyes. The number of accumulated leukocytes in LHP-treated eyes started to increase at 12hr, and peaked at 24hr which was significantly higher than in both control and vehicle-treated eyes (P<0.01). The number of accumulated leukocytes in the PEG-SOD-treated rats was reduced by 88.0% at 24hr (P<0.01). Intravenous injection of PEG-SOD significantly inhibited the leukocyte rolling and its accumulation under LHP-induced oxidative stress. These results suggest that PEG-SOD might attenuate various retinal microcirculatory disorders associated with LHP.