Abstract
A variant, derived from both measles and subacute sclerosing panencephalitis virus preparations, incapable of producing intercellular fusion or syncytia typical of measles virus infections is described. This non-syncytiogenic (N-S) virus was easily detected using immunofluorescence, was genetically stable and replicated autonomously. The variant was defective in the production of both infectious virus and haemagglutinin in Vero and Hep2 cells. Persistent infections in Hep2 cells were readily established without the cooperation of defective interfering particles or temperature-sensitive mutants, although interferon could be detected. It is possible that such N-S variants may be involved with the regulation of persistent infections by measles virus.