The author has discussed such problems as: sources of fluorine in the biosphere, assimilation and accumulation of fluorine in plants, distribution of fluorine in a plant, phytotoxicity of fluorine and the application of the phyto-physiological index in the monitoring bioindication. The investigations were carried out in a period of the full operation of the Aluminium Works at Skawina near Cracow and after its closing down at the beginning of the eighties. After the Works had been closed down the level of fluorine in the leaves of the tested gladioli was in the limits of the physiological content, and it was 16 times lower than in the period of the full operation of the Works.