Fluoride was measured in samples of lichen and grass collected in 1987 from over 50 sites on the slopes of Mt. Etna. Raised levels of fluoridewere detected on the downwind, eastern side, indicating that the volcano’s plume is the principal source of the fluorides. Lichens proved to be more sensitive than grasses in determining the dispersal of the plume; volcanogenic fluorides were detected in the grasses over a more limited area. The fluoride levels in the lichens range from 3 to 141 ?g/g, whereas the range in the grasses is 3 to 62 ?g/g. These concentrations are comparable with those obtained from industrial sources and indicate that the fluoride emitted by the plume are a potential environmental hazard.