The experiments of a number of careful investigators have discredited the claims made for ozone as a purifier of air. Largely on the basis of claims already disproved, several manufacturers are so successful in introducing ozone machines into public buildings that this purposeful adulteration of the air with ozone and its accompanying impurities threatens to become a public health problem.Ohlm\l=u"\ller1 demonstrated that ozone in considerable strength was incapable of killing dry bacteria within the time-limits of his tests. Erlandsen and Schwarz2 showed the falsity of the claim that the presence of free ozone means the absence of organic impurity in the air. They demonstrated, through careful analyses, that ammonia and hydrogen sulphid were not diminished in amount by the presence of ozone. They showed also that the