Four of positive clones were obtained by three runs of screening the cDNA library of human liver with rabbit antihuman apolipoprotein (apo) CIII IgG. One of them was identified to be the positive clone of apoC III cDNA by restriction endonuclease map studies of the cDNA insert fragment and by Western blot analysis of the expression products. The apoCIII cDNA-gamma gt11 recombinant DNA prepared from the positive clone can be used in RNA-dot blot analysis as apoCIII cDNA probe. And the apoCIII cDNA clone can be also used to produced apoCIII peptide under the induction of isopropyl-beta-D-thiogalactoside. The apoCIII peptide, after purification, has a lot of use in further studies.