Abstract The complete nucleotide sequence of RNA segment 4 of influenza C/JHB/1/66 virus has been determined, utilizing cloned cDNA derived from the viral RNA segment. The gene is 2073 nucleotides in length, and can code for a polypeptide of 655 amino acids, which corresponds to the viral glycoprotein. The predicted polypeptide has a molecular weight of 72063, not including oligosaccharides linked to eight predicted glycosylation sites. The influenza C glycoprotein shares structural features with hemagglutinin (HA) glycoproteins of influenza A and B viruses, including three stretches of hydrophobic amino acids believed to function as a signal sequence, a fusion function, and a membrane anchor. However, a substantial part of the protein lacks direct sequence homology to these HA glycoproteins. The results suggest a more distant evolutionary relationship between influenza C virus and influenza A and B viruses, compared to that between influenza A and B themselves.