Hypocholesterolaemic agents are powerful modifiers of the plasma lipoprotein pattern. In addition to lowering plasma low density lipoprotein (LDL) cholesterol, such drugs may elevate, decrease or have no effect on high density lipoprotein (HDL) cholesterol. Bile acid binding resins and 3-hydroxy-3-methylglutaryl Coenzyme A (HMG-CoA) reductase inhibitors cause a reduction in hepatic cholesterol content resulting in stimulation of LDL receptor activity. This decreases the plasma LDL level, while HDL cholesterol levels remain unchanged or increase. Probucol, on the other hand, lowers both LDL and HDL cholesterol. It does not act by stimulating LDL receptor activity and is effective in some patients with homozygous familial hypercholesterolaemia who virtually lack LDL receptors. Despite their different lipoprotein-modifying effects, both HMG-CoA reductase inhibitors and probucol are regarded useful in the prevention and retardation of atherosclerosis.