For preparation of a multielement lichen reference material for environmental studies, 25 kg of the epyphitic lichen Evernia prunastri (L.) Ach. was collected in unpolluted regions of Portugal. The lichen was removed from Cistus ladanifer and Quercus spp. The material was ground to a mesh size 125 m. The material homogeneity was evaluated by determining Na, K, Mn, Br, As, La and Sm on two samples of 100 mg taken at each of 20 locations of the bulk material; the locations were randomly chosen. The k0-based INAA was used. The material is homogeneous for fractions 100 mg, as shown by the evaluation of the heterogeneity of the subsampling operation in the 20 locations and by the results of a one-way analysis of variance for the data obtained. The composition of Evernia prunastri varies neither with the region where it grows nor with the date of collection. This work was accomplished under contract with the IAEA.