A full-length cDNA clone for apolipoprotein CIII has been isolated from a human fetal liver cDNA library constructed in the vector lambda gt10. The clone spans 677 nucleotides, including a 48-bp 5'-untranslated segment, 300 bp of coding sequence, and a 276-bp 3'-untranslated segment. The deduced amino acid sequence includes a 79-amino acid mature polypeptide and a 20-amino acid amino-terminal signal sequence. The signal sequence was compared with those of other lipoproteins.