The principal events of the pandemic of Asian strain influenza can be discussed and studied in chronological form, although it is unlikely that the point of origin will ever be precisely located. The disease was first reported in late February, 1957, in China. From established foci in countries along the eastern fringe of Asia the disease spread to many new areas in May. North America, northern South America, and Europe experienced widespread Asian strain influenza epicemics before the month of September was over. It would seem that the most important timing factor for epidemic occurrence in the equatorial regions was the presence or absence of the virus in sporadic cases. In regions where seasons are well marked the situation was much more complex. In the regions far from the equator, greater crowding and more opportunities for close contact are more likely to in fall and winter. The apparent shortening of time necessary for world-wide spread in the most recent pandemic reflects the speed and extent of modern travel.