A clinical double blind trial on 98 volunteers was undertaken with the aid of the SB Index to show the effects on the gum of a tooth paste containing detergents. It resulted in a significant increase of the SBI after 6 weeks of a tooth paste with a high content of surface active substances. With the light microscope changes are demonstrable in the Stratum spinosum which could be identified electron-microscopically as a strong increase of bundles of filament in the cytoplasm. The contradiction between clinical and morphological findings is explained by the assumption that the greatincrease in filament bundles leads to a lowering of the adaptability of the epithelium and consequently to increased tendency to bleed, especially in response to mechanical irritation.