It has often been observed by clinicians that certain patients with paralytic poliomyelitis give a history of severe exertion immediately preceding the onset of paralysis. The inference has been that perhaps undue exertion in some way precipitated the paralysis. Trauma preceding onset has also been mentioned as a possible predisposing cause. Recently it has been postulated on both clinical and theoretic grounds that physical activity at a crucial time might be one of the factors which determines the degree of spread of virus in the central nervous system and therefore the severity of the disease.1Levinson, Milzer and Lewin studied experimentally the effects of fatigue, chilling and mechanical trauma during the incubation period on the resistance of rhesus monkeys to poliomyelitis.2They found that the incidence and severity of paralysis was greater in monkeys subjected to exhausting exercise or chilling than in control animals; no correlation was demonstrated