Summary: Of the filtrates from 54 throat washings tested by the chick embryo passage method 28 gave evidence of containing influenza virus. The strains were isolated directly in chick embryos, and the presence of hemagglutinins in the allantoic fluid was used as evidence for the presence of influenza virus. In most instances where a successful isolation was obtained, the positive result was first noted in the 2nd embryo passage. Inoculation of strains that had been isolated by this method, into mice, ferrets, and chick embryos, showed their capacity to infect ferrets and embryos in high titer, but they possessed a very low order of virulence for mice.