Because reactive oxygen species are formed during the metabolism of several toxins that cause similar pathologic changes, we hypothesized that compounds that alter the concentration of reactive oxygen species would alter the toxic effects of the peptide-hepatotoxin produced principally by Microcystis aeruginosa. Pretreatment with alloxan, butylated hydroxyanisole or desferrioxamine did not alter the severity of microcystin-LR intoxication in fed mice. Furthermore, fasting mice for 24 hr before testing, which unmasks lipid peroxidation in paracetamol intoxication, did not alter the effect of butylated hydroxyanisole pretreatment.