Oxidative modification of low density lipoprotein (LDL) renders it more atherogenic. Probucol, a highly nonpolar antioxidant, is transported in lipoproteins, including LDL, and inhibits oxidative modification of LDL in vitro. The ability of probucol to inhibit atherogenesis in the LDL receptor-deficient rabbit has been attributed to its antioxidant effect. We report synthesis of a new water-soluble analogue of probucol that is very effective in preventing cell-induced LDL oxidation. The polar probucol derivative, diglutaryl probucol, is efficiently taken up by endothelial cells and macrophages in culture and is hydrolyzed to release the active antioxidant, probucol. The treated cells, after thorough washing, show a marked decrease in their capacity to oxidize LDL during a subsequent incubation. At high concentrations of the derivative, the cells also released free probucol into the medium. Thus, the effectiveness of probucol in vivo may be related both to its presence in LDL, acting as a nonspecific antioxidant, and to an additional ability to inhibit cell-mediated oxidation of LDL by virtue of its uptake into cells.