Lichens were surveyed at 128 sites around a coal-fired power plant in an unurbanized region of southeastern Ohio. Corticolous lichens were found to be useful indicators of air quality while terricolous and saxicolous species were not. Mapping revealed void areas in the distribution of Parmelia caperata (L.) Ach. and P. rudecta Ach. The area of affect was smaller than most of those re- ported for cities, and in this hilly region, site elevation was found to be an impor- tant factor influencing lichen distribution. Many previous studies have related disappearance of lichens to a deterioration of air quality in cities. These studies have been done around large urban and industrial areas, primarily in Europe and Canada. The recent book edited by Ferry et al. (1973) contains an excellent summary of lichen studies to date. Most workers agree that the disappear- ance of lichens as an industrial area is approached correlates with an increase in atmo- spheric sulfur dioxide (SO,). However, the situation in urban and industrial areas is very complex. Smoke is emitted from a number of low-level sources, and usually con- tains a mixture of phytotoxic compounds. In addition, city factors such as lower humid- ity, higher temperatures, and lower availability of suitable substrates are also present. These variables create a very complex system and meaningful conclusions are indeed difficult to obtain. Studies done around unurbanized emissions sources have the potential of yielding more information, but studies of this type are few. Skye (1958) and Rao and LeBlanc (1967) have shown that lichens decrease around isolated factories that emit primarily SO,. In a recent study, Nash (1972) found that species diversity is markedly reduced near an isolated zinc factory where both SO2 and zinc are released. With the growing interest in air quality and the use of lichens as natural indicators, more studies in areas without city effects are in order. This study was conducted in an unurbanized area around a coal-fired power gener- ating plant. Muskingum Plant is located adjacent to the Muskingum River, above the town of Beverly, in southeastern Ohio (Fig. 1). The nearest city is Marietta, Ohio, 17