The adenovirus hexon protein has been carboxymethylated with 14C-labeled iodoacetate. After treatment with CNBr, the peptide mixture was fractionated into fragments with seven size classes by exclusion chromatography. Large fragments were further purified by CM-cellulose chromatography in urea, and small fragments were purified by high voltage paper electrophoresis. Amino acid sequences of pure fragments have been determined by combined use of sequenator-based direct degradations, and of manual t-dimethylaminonaphthalene-1-sulfonyl-monitored Edman degradations subsequent to enzymatic redigestions. Fractionations are given, the primary structures of 22 CNBr fragments containing a total of 677 residues are reported, and the analytical aspects of the structural properties are considered.