The object of this work was to see if there is any relation between the oxidation-reduction conditions existing in a plant, and its ability to grow successfully in the cities where air contains H/sub 2/S. Oxidation-reduction potential, capacity for its water-soluble and insoluble matter to be oxidized with KMnO/sub 4/ before and after treatment with H/sub 2/S, and finally the effect of the age of the plant were determined for different spp. of several common families of plants. In the majority of the families it was found that in various spp. of the same family these characteristics vary within a narrow and different range. Oxidation with KMnO/sub 4/ of the water-insoluble matter was found to be the best criterion of the sensitivity of a plant to H/sub 2/S.