Volcanoes are known to discharge gaseous fluorides to the atmosphere, but measurement of these is difficult, and the dispersion characteristics have not previously been studied in detail. Samples of lichens were collected from the slopes of Etna Volcano in 1985 and 1987, in order to monitor these gases. Subsequent analysis for fluoride showed levels ranging from 2 to 141 μg g−1, compared with control values of < 2 μg g−1 The fluoride accumulation patterns clearly show that there is a major input from the volcano's plume, with the highest levels on the downwind side; these are attributed to the prevailing winds and to the local topographic influences. The fluoride levels in the lichens are compared with those resulting from industrial pollution.