Derek Smith, Professor of Infectious Disease Informatics, University of Cambridge, U.K., has developed a method for visualizing antigenic evolution by creating two-dimensional maps in a process called antigenic cartography. These maps are made with data that provide information on the antigenic properties of the pathogen. In the case of influenza virus, the data come from measuring the ability of an antiviral antibody to inhibit hemagglutination – binding of virions to red blood cells. Such maps show how amino acid changes can affect antibody binding to virus particles, which cannot be done by comparing nucleotide sequences of different virus isolates. By charting influenza virus strains in this way, it should be possible to better understand genetic and antigenic evolution.