IT IS AN HONOR and responsibility to present this Tenth Annual Don W. Gudakunst Lecture. Dr. Gudakunst, as first Medical Director of the National Foundation for Infantile Paralysis, was administrator and participant in a productive research program. In 1950, the year Dr. Charles Armstrong gave the first Annual Lecture, the program received new impetus with results now familiar to us all. The list of distinguished lecturers of succeeding years, including Sabin, Bodian, Paul, Salk, Enders, Francis, Horstmann and Huebner, is a record of workers and achievement that opened the way to control of poliomyelitis, and vastly expanded our understanding of viruses, nucleic acids, cells, and their interaction to produce cellular infection. Dr. Gudakunst would be proud of his early association with and contribution to the research program which continues under generous support of The National Foundation. Apart from its record of outstanding contributions to prevention of poliomyelitis, this annual series of lectures is evidence that the distinction between pure and applied research has less and less meaning. With this example before me, in discussing enteroviruses I shall proceed freely from epidemiologic to basic research. Work done at Minnesota represents contributions of a group of associated investigators. THE ENTEROVIRUS TRIBE In the days when our virologic tools were limited, we used to speculate that the human environment might include many viral nonpathogens or opportunist pathogens, as well as the viruses of known diseases. Study of the enteroviruses illustrates technologic advances achieved since 1950, to uncover more than 100 viruses now characterized, and many others unidentified but distinguished from known types.