The structural features responsible for the immunogenicity of certain parts of native protein molecules have been of interest to immunochem ists and protein chemists for over three decades. However, until re cently no concerted effort was (or could be) devoted to the elucidation of the complete antigenic structure of a protein. In order for these en deavors to be successful and meaningful, knowledge of both the amino acid sequence and the detailed three-dimensional structure of the protein is necessary. Such information was not available for a protein until early in the 1960s. This and the...