Bepridil, a calcium antagonist with anti-anginal, anti-ischemic, and anti-arrhythmic properties was assessed for its ability to scavenge free radicals. Bepridil reduced the stable free radical 1,1-diphenyl-2-picrylhydrazil (DPPH) in the molar ratio 2:1 and, in this respect, was as active as the reference anti-oxidants hydroquinone and alpha-tocopherol. Allopurinol and SOD inhibited cytochrome c reduction in a hypoxanthine-xanthine oxidase superoxide generating system, whereas bepridil was ineffective. Deoxyribose degradation induced by the .OH radical was prevented by bepridil (IC50 = 0.050 mM). This ability to scavenge .OH was similar to that of dimethyl sulfoxide (DMSO) (IC50 = 0.056 mM) and more potent than that observed with mannitol and allopurinol (IC50 values of 0.74 mM and 0.92 mM, respectively). The powerful .OH scavenging activity of bepridil was confirmed in vivo on alloxan induced diabetes in mice. Bepridil exerted a marked protective effect at 0.150 mmol/kg whilst, ethanol and DMSO were active at the doses of 90 and 94 mmol/kg, respectively. These results demonstrate that bepridil is a potent .OH radical scavenger. This property may contribute to the therapeutic activity of this drug in myocardial ischaemia.