SummaryDuring a period of 30 days' continuous cultivation of the Melbourne strain of influenza A virus in roller tubes, the respective titers of virus in the chick embryo tissue and fluid components after initial increases remained almost constant, provided the fluid contained serum and embryonic extract. When Tyrode solution or physiological saline was substituted, the amount of virus declined gradually after one week. The virus grew well in cultures of various organs from 14-day chick embryos except in the case of brain, heart and skeletal muscle.