Thalli of five species of epiphytic lichens were collected from one moribund spruce-fir stand in the Algonquin Highlands in Ontario, Canada. Extracts of all were subjected to isoelectric focusing and stained for activity of 16 enzyme systems. Gels were scored for the presence or absence of individual bands in each enzyme system, and the degree of polymorphism of all detectable enzymes was evaluated using a variability measure developed for use with presence/absence data. Esterase and alkaline phosphatase showed the greatest amount of polymorphism and superoxide dismutase was the least variable enzyme system. The degree of enzyme variability in each of the five species was probably a reflection of its past evolutionary history and bore little relationship to apparent potential for sexual reproduction.