Tmmunity in poliomyelitis is a particularly timely topic in view of recent studies from many laboratories. The theme of immunology presented here, however, will be launched from a series of events occurring on the small Pacific island of Guam, and subsequently subjected to laboratory and armchair analysis. No attempt will be made to review much of the older literature on the immunity of poliomyelitis. As an excuse, a cue will be taken from Dr. Sabin, who said at the end of a Bela Schick Lecture (1), "I have drawn largely on my own studies, and may have left the impression that very little other work has been done on the subject that is worth mentioning". Then he quoted Professor Szent-Gyorgi who, when challenged at the end of a lecture by another scientist for not having mentioned his work, replied: "If I had taken time to describe his many contributions, I should have had no time left to tell of my own." Articles about poliomyelitis are characterized by two common faults of popular medical subjects: excessive quantity and frequent lack of quality. The tremendous amount of trash cluttering up the literature renders all polio work most difficult. Rather often work of poor quality casts doubt on sound conclusions based on perfectly good work, but to remove the doubt it must be repeated, some times not just once but several times. The thousands of published articles nevertheless do include scores of reports of excellent work. In fact, the writings of Caverly, Flexner, Landsteiner, Wickman, Frost, Aycock, Trask, and many others provide precedent for practically every idea and every experiment reported since. Amateur scientists, however, many seeking easy publicity, have written profusely on poliomyelitis on the slightest scientific pretext. Before launching into the subject of immunity in poliomyelitis, certain concepts should be clarified. First, infection with the virus of poliomyelitis must be clearly distinguished from the recognized paralytic or nonparalytic disease. Practically everyone eventually, and frequently very early in life, becomes infected with the several viruses, which we call poliomyelitis viruses, but the clinical syndrome called poliomyelitis is a rare manifestation, perhaps only a "complication" of these infections. Second, it is quite possible that the factor of resistance which prevents the majority of persons from manifesting central nervous system disease or "complication" during infection is not immunity, for in poliomyelitis this non-specific factor of resistance presumably is ordinarily present at the time