In 30 atherosclerotic patients different serum analytes and neopterin concentrations in serum and urine were determined before and after Heparin-Induced Extracorporeal LDL and Fibrinogen Precipitation therapy. Neopterin concentrations in serum of all 30 patients were increased (mean=9.18 nmol/l, SD=3.23) compared to age matched healthy people (mean=5.34 nmol/l, SD=2.70) and were significantly lowered after H.E.L.P therapy (mean=S.22 nmol/l; SD=3.22, p=0.002, t-test) . These results suggest the involvement of the cellular immune system in the occurrence of atherosclerosis. Further neopterin, the macrophagederived immune activation marker, is significantly correlated with fibrinogen (linear correlation coefficient r=0.36, p=0.05). Long-term neopterin concentrations in serum of 4 patients (three with coronary heart disease and one with Papilla edema), from the first up to the 9th, respectively 12th therapy decreased, in contrast to fibrinogen which stayed stable or even increased during long-term treatment.