RNase activity in Lasallia hispanica, Parmelia omphalodes and Cornicularia normoerica collected at different times and in different habitats, have shown variability that cannot be solely attributable to variation in habitat or season. Electromorph pattern of RNase activity in L. hispanica and C. normoerica, showed variations among different collection times; some bands are constant but other showed high variability, which could be related to physiological changes. It is also noteworthy that in both species one band is exclusively present in thalli from one of the sampling localities. This could be the result of an adaptation to this habitat and/or due to genetic differences.