Free radicals have recently been proposed to play a role in the development of diabetic retinopathy. Ischaemia and hyperglycaemia followed by recirculation have been suggested to initiate free radical production in other tissues and the aim of the present study was to examine whether this could also be the case in the retina. The present study showed retinal cell damage, as measured by pycnotic cells, to be more pronounced when ischaemia was combined with hyperglycaemia than when combined with normoglycaemia. As an indication of free radical production, catalase activity was measured, reflecting the production of hydrogen peroxide (H2O2). Small amounts of H2O2 were found to be generated in the normal retina, but did not increase during ischaemia and hyperglycaemia followed by recirculation. It thus seems, as if hyperglycaemia aggravates the harmful effects of ischaemia, but with the methods used, there does not seem to be any increase in free radical production (as measured by H2O2 production) in normal rat retina during ischaemic and hyperglycaemic conditions.