Aim Endothelial cells injured by free radicals is a crucial step in tbe development of many diseases. We investigated the protective effect of probucol. an an-tiatherosclerosis drug,to the cultured hurnan endothe-lial cells.Methods The oxidized low density lipoprotein (OLDL) were used as free radial resources and 'H-TdR incorporation of the cells was estimated as DNA sgnthesis. The microstructure change was studied by using the scanning electron misroscope.Results At 24 hours interval, the k-TdR incorPo-rated into the cells in OLDL group was 48K as that of nLDL group or 56K as that of probucol + OLDL group (p<0.001 ). The scanning electron micro-scopic study showed that the intercellular junctions di-ndnished and the cellular outline changed in the OLDL treated cells but not the probucol treated cells.CoarIasloas Probucol is an useful antioxidant in preventing the cultured cells from injury by free radi-cals and perhaps tbus contributes to the antiathero-genesis effeCt.