The role of HDL and its main protein component the apolipoprotein A-l as being antiatherogenic is well established. Experimental data give support for the involvement of at least three different types of mechanism: (1) the reverse cholesterol transport, (2) anti-inflammatory mechanisms and (3) antithrombotic mechanisms. Depending upon the stage and type of atherosclerosis, different mechanisms may be more or less important. Knowledge of pharmacology of apolipoprotein A-l has strongly increased during past years and clinical studies have started with infusions of apolipoprotein A-l phospholipid complexes.