The present work describes a procedure for determining apolipoproteins (apo) B-100 and B-48 in subfractions of triglyceride-rich lipoproteins by analytical sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) with Coomassie staining. The chromogenicity of the two apoB species was found to be almost equal, and independent of lipoprotein particle size. Both proteins were sensitive to overloading of the gel, which resulted in low dye uptake. This was particularly evident for apoB-48. The precision of this analytical SDS-PAGE-based procedure to determine the plasma concentrations of apoB-100 and B-48 in triglyceride-rich lipoproteins was found to be appreciably low (coefficients of variation ranging between 3.1 and 14.1%).