THERE is considerable clinical evidence to show that in persons infected with malaria various stimuli may precipitate an acute attack. These stimuli include surgical operations, the injection of vaccines, exposure to cold, and possibly, for persons who have not become acclimatized, ascent to high altitudes. There is also evidence, both clinical and experimental, to show that injections of cortisone increase the virulence of bacterial and virus infections. Trypanosome infections also, including Chagas's disease, are intensified in animals given cortisone1,2.