The relative roles of the superoxide and hydroxyl radicals in oxidative stress-induced neuronal damage were investigated using organotypic hippocampal slice cultures. Cultures exposed to 100 microM duroquinone, a superoxide-generating compound, for 3 h developed CA1-selective lesions over a period of 24 h. The damage accounted for approximately 64% of the CA1 subfield, whereas CA3 showed just 6% damage, a pattern of damage comparable to that observed following hypoxia/ischaemia. Duroquinone-induced damage was attenuated by a spin-trap agent. In contrast, hydroxyl radical-mediated damage, generated by exposure to 30 microM ferrous sulphate for 1 h, resulted in a CA3-dominant lesion. The damage developed over 24 h, similar to that observed with duroquinone, but with approximately 45% damage in CA3 compared with only 7% in CA1. These data demonstrate a selective vulnerability of the CA1 pyramidal neurones to superoxide-induced damage and suggest that of the free radicals generated following hypoxia/ischaemia, superoxide, rather than hydroxyl radical, is instrumental in producing neuronal damage.