To test whether impaired glutathione redox status may be related to lens oxidative damage in humans, we measured glutathione (total and oxidised forms) and malondialdehyde, a lipid peroxidation product, in clear lenses and diabetic and non-diabetic cataracts. Diabetic cataracts were divided into 2 subgroups with either intact or abnormal haemo-ocular barrier as evaluated by preoperative iridography. Decreased total glutathione values were observed in cataractous (diabetic and non-diabetic) as compared to clear lenses (p < 0.001), whereas enhanced oxidised glutathione levels were found in diabetic caracts as compared to non-diabetic ones and clear lenses (p < 0.001). Malondialdehyde concentrations were significantly higher in all types of cataracts, especially myopic and diabetic ones, than in clear lenses (p < 0.001). Moreover, malondialdehyde levels in diabetic lenses were inversely correlated with total glutathione (r = 0.80; p < 0.001) and linearly correlated with oxidised glutathione values (r = 0.76; p < 0.001). Finally, glutathione redox status was found to be more seriously impaired in lenses from diabetic patients with abnormal than intact haemo-ocular barrier. These data suggest a contributory role of lipid peroxidation and glutathione oxidation and consumption in the pathogenesis of cataract, especially in diabetic lenses with haemo-ocular barrier abnormality.