In the lichen Acarospora schleicheri collected in altitudinal gradients at 18°S, 19°S, and 33°S in alpine zones of Chile, the concentrations of rhizocarpic acid were determined and compared. Significant increments in the accumulation of rhizocarpic acid were observed at the highest altitudes and they were correlated with the increasing UV-B radiation levels in the selected gradients. The results obtained suggest that the synthesis of rhizocarpic acid is induced by UV-B radiation, and that this lichen compound represents a chemical adaptation to the high levels of UV-B radiation in lichen habitats