Conn studied fourteen severely ill patients, ranging in age from fourteen to thirty-five years, in the Respirator Unit of the Children's Hospital School in Baltimore. A characteristic personality was delineated and correlations attempted between this and the course of the poliomyelitis. The rather typical patient showed marked inhibition in aggression and self-assertiveness, a compulsive need to please others, and pronounced fear of failure, all resulting in a tendency to compulsive overactivity and overexertion in an effort to secure approval. This character type helps to explain the overexertion and overfatigue that frequently precede the attack of poliomyelitis. These patients are deprived of the safeguard against extreme exertion normally provided by a sense of fatigue. This is one of several factors that may contribute to breakdown of the protective mechanisms against illness. This hypothesis, based on only a few cases, deserves further study for confirmation.