Free radical (FR) mediated oxidation of low density lipoproteins (LDL) has been implicated in atherogenesis. Probucol is a lipid lowering agent with antioxidant properties which may protect the LDL from FR mediated damage. The specific mechanism by which probucol acts as an antioxidant has not previously been reported. We therefore studied the FR scavenging properties of probucol in vitro and results show that this drug is a powerful superoxide scavenger. This property may be relevant in its use as a lipid lowering drug in the retardation of the atherosclerotic process.