Foci of degeneration produced by measles virus in cell cultures with antibody-free liquid medium

Measles virus produces discrete foci of degeneration in monkey kidney cell and HeLa cell cultures with antibody-free liquid medium. The number of sharply defined “foci” is directly proportional to the relative virus dilution. The technique for enumeration of infective units of measles virus by “foci” count is described. The self-limiting spread of measles virusin vitro and some possible advantages over the standard plaque method are discussed.