A highly dense subclass of the high-density lipoproteins, with particle sizes below 7 nm. They are also known as nascent HDL, composed of a few apolipoprotein a-i molecules which are complexed with phospholipids. The lipid-poor pre-beta-HDL particles serve as progenitors of HDL3 and then HDL2 after absorption of free cholesterol from cell membranes, cholesterol esterification, and acquisition of apolipoproteins a-II, Cs, and E. Pre-beta-HDL initiate the reverse cholesterol transport process from cells to liver.