Oxysterols are oxygenated derivatives of cholesterol and related compounds.One interesting biological property of these compounds is that they are cytotoxic to a wide variety of cells at micromolar concentrations. The mechanism of this cytotoxic activity is unknown. Using cell cultures, our laboratory attempts to examine the biochemical basis of the cytotoxic effect of these compounds. The potential importance of these studies is that oxysterols may play a major role in the pathogenesis of atherosclerosis as components of oxidized low density lipoproteins.