Components of human serum can be separated on the basis of differences in relative molecular mass by using size-exclusion 'high-performance' liquid chromatography. Lipoproteins in fractions of the eluate can be quantitated by conventional chemical and enzymatic methods. Alternatively, if lipoproteins in the serum are selectively presented with diformazan dye, the column effluent can be monitored spectrophotometrically at 580 nm, so that only the lipoprotein components of serum are detected. Samples of purified low-density lipoproteins, so stained and analyzed, provide peak-area values that are proportional to their concentration as evaluated by chemical methods. With this technique, the various lipoprotein classes can be quickly separated and their concentration estimated. These techniques should prove useful in clinical and research laboratories.