AbstractSporidesmin, the mycotoxin responsible for ‘facial eczema’ in ruminants, has previously been shown to generate superoxide radical and hydrogen peroxide. In the present study, the formation of the third ‘active oxygen’ species, hydroxyl radical, has been demonstrated. This species is produced both during the autoxidation of the reduced (dithiol) form of the mycotoxin and in the cyclic reduction/autoxidation reaction between sporidesmin and glutathione. In view of the exceptional reactivity of the hydroxyl radical, this substance may be the proximate agent responsible for the toxic effects of spor