The clinical application of a new extracorporeal procedure (HELP) for the selective elimination of low-density lipoproteins and fibrinogen by heparin precipitation at acid pH is described. Plasma, obtained by filtration of whole blood through a 0.2 micron filter is continuously mixed with an equal volume of an acetate buffer (pH 4.85) containing heparin. After removal of the precipitated heparin complex by filtration, excess heparin is adsorbed to a specially developed filter, and the clear plasma filtrate is subject to bicarbonate dialysis/ultrafiltration to restore physiologic pH and remove excess fluid. The calculated efficiency for the elimination of low-density lipoproteins and fibrinogen from plasma by HELP is 100% and is therefore comparable to conventional plasmapheresis. However, the HELP system shows a high degree of specificity, with over 80% of total protein being returned to the patient. A total of over 350 treatment procedures have now been performed. Patient compliance and acceptance have been excellent, and no major complications have been observed. The system is therefore suitable for the treatment of severe hyper-beta-lipoproteinemia; its use for the treatment of coronary heart disease is currently under investigation in a prospective multicenter study in which treatment efficiency will be controlled by coronary angiography on 45 patients treated with HELP over a period of 2 years.