The aim of the present study was to develop a standardised protocol for the use of Lolium perenne cultures to biomonitor the surroundings of an aluminium smelter. Five ecological stations, which corresponded to air quality network monitoring sites pertaining to the smelter, were selected for study. Cultures of L. perenne (one at each site) were exposed for approximately 28 days, at different times between August 1999 and October 2000. At the end of the exposure periods, the fluoride concentrations in the cultures were determined. The concentrations of fluoride determined in the L. perenne cultures varied from 4.32 microg g(-1) to 912.22 microg g(-1) and followed a similar trend to concentrations of atmospheric fluoride. However, a wider range of fluoride concentration was observed in the L. perenne cultures than in the air surrounding the smelter. The background levels of fluoride in L. perenne cultures were also calculated, thereby allowing classification of fluoride air pollution in the area under study.