In 1986, Young et al. reported the presence of a truncated apolipoprotein (apo) B in the plasma of the members of kindred with hypobetalipoproteinemia. Subsequent studies revealed that the truncated apoB was caused by a frameshift mutation in the apoB gene. Since then, it has become apparent that a variety of apoB gene mutations that interfere with the translation of a full-length apoB-100 molecule can cause familial hypobetalipoproteinemia. Many of these mutations result in the production of a truncated species of apoB that can be detected within the plasma lipoproteins. A comprehensive review of familial hypobetalipoproteinemia that includes a summary of the historical aspects of the syndrome, clinical descriptions of the heterozygous and homozygous forms of the disorder, a list of apoB gene mutations, causing hypobetalipoproteinemia, and a summary of the properties of lipoproteins, containing truncated apoB species has been published. This chapter describes the techniques that are useful in identification and characterization of truncated apoB species.