Fluoride is among the most phytotoxic atmospheric pollutants, commonly linked to the appearance of lesions in susceptible plants around emitting sources. In order to assess the effects of fluoride on leaves of Spondias dulcis Parkinson (Anacardiaceae), plants were examined 78 km (non-polluted area) and 0.78 km (polluted area) from an aluminium smelter. The level of fluoride increased with the exposure time of the plants in the polluted area. On the third day of exposure in the polluted area, necroses with typical colouration were observed. Micromorphological damage began at the abaxial epidermis, mainly associated with the stomata. Starch grain accumulation was more pronounced in the midrib. The cell membranes and chloroplasts were greatly affected by the pollutant. We observed accumulation of phenolic compounds and electron-dense material at the boundaries of the ending veinlets. The microscopic events described precede the appearance of symptoms and are therefore of prognostic value in predicting injury by fluoride and will be useful as biomarkers. The high sensitivity of S. dulcis to fluoride and the specificity of the symptoms confirm, for the first time, in an experiment of active biomonitoring, the potential of this species as a bioindicator.