An application of SDS gradient polyacrylamide slab gel electrophoresis to the analysis of lipoprotein polypeptides is described. The 10-15% polyacrylamide gradient provides a high degree of resolution and sensitivity resulting in a single separation of the major apoproteins which can be easily visualized. When combined with autofluorography, individual protein mass and radioactivity can be determined densitometrically while still retaining excellent resolution. Examples of rat lymph and plasma apolipoproteins are shown, and apparent heterogeneity of certain apoprotein subgroups is described.