Micro-PIXE was applied in the study of arsenic metabolism in the lichen Hypogymnia physodes (L.) Nyl. Lichen thalli were laboratory exposed to a solution of an inorganic arsenic compound arsenate and to a control solution. Perpendicular sections that reveal the morphological properties of the lichen thallus were subjected to microbeam measurements to obtain data on the localization of arsenic and its influence on the distribution and concentrations of the selected macro- and microelements P, S, K, Ca, Cl, Mn, Fe and Zn. Five groups of elements were distinguished regarding losses and redistribution due to arsenic exposure: (1) K and Ca were depleted from all lichen layers; (2) Mn was depleted from the algal layer and lower cortex, (3) Fe was decreased in the algal layer and increased in the lower cortex, (4) Zn was decreased both in the algal layer and the medulla, but increased in the lower cortex, and (5) P and S were decreased in the medulla, but increased in the algal layer and the lower cortex.