When tested on Vero cells the Edmonston strain of measles virus contained a mixture of plaque variants and variants which produced different kinds of cytopathic effect under liquid culture. A persistently infected culture of HEp2 cells which was derived from the Edmonston virus yielded low titers of infectious virus and was temperature sensitive (Gould, 1974). This persistent virus was less heterogenous than the parent Edmonston strain as judged by plaque morphology and type of cytopathic effect produced under liquid culture.