Sendai virus was concentrated from the allantoic fluid of embryonated chicken eggs by polyethyleneglycol (PEG) precipitation. A concentration of 6–8% PEG sufficed to precipitate essentially all of the virus (measured by hemagglutination) with maximum retention of cell-fusion ability. Electron-microscopic examination of the 6% PEG pellet revealed only intact virions. Thus the method is suitable for preparing Sendai virus for cell-fusion experiments.