A convenient method for the quantitation of choline-containing phospholipids in each lipoprotein fraction has been developed by combining separation by high-performance liquid chromatography with gel permeation columns and selective detection by enzymatic reaction in the post-column effluent. The elution patterns monitored by choline-containing phospholipids were compared with those monitored by cholesterol. The elution patterns of choline-containing phospholipids were found to give much more information about the distribution of lipoproteins according to their particle-size differentiation than analyses done by cholesterol. This choline-containing phospholipid monitoring method not only resolves lipoprotein peaks of the major classes (chylomicron + VLDL, LDL, HDL2 and HDL3) quantitatively, but also detects the presence of abnormal lipoproteins containing a large amount of choline-containing phospholipids. We could detect these abnormal lipoproteins using a small amount of whole serum (10-20 microliter) from patients with various liver diseases. Our examination of HDL subclasses using this technique showed that the HDL fraction was composed of several subfractions due to their particle-size differentiation.