The concentration of five different elements in six lichens species of different regions in Giresun and Ordu (Turkey) was determined using the energy dispersive X-ray fluorescence method. A radioisotope excited Xray fluorescence analysis using the method of multiple standard addition is applied to the elemental analysis of lichens. An annular 50 mCi Am-241 radioactive source and an annular 50 mCi Fe-55 radioactive source were used for excitation of characteristic K X-rays. An Si(Li)detector which has a 147 eV full-width at half-maximum for 5.9 keV photons was used for intensity measurements. A qualitative analysis of spectral peaks showed that the samples contained potassium, calcium, titanium, iron, and barium. (c) 2005 Elsevier Ltd. All rights reserved.