Following our previous reports of extracellular laccase activity in lichenized ascomycetes, we investigated the diversity of laccase isoforms in lichens in 20 species from the suborder Peltigerineae. The molecular masses of the active forms of most laccases varied between 135 and 190 kD, although some lichens within the family Peltigeraceae had laccases with higher masses, typically varying from 200 to over 350 kD. Size exclusion chromatography (SEC) was used to confirm the accuracy of the electrophoretic estimates of molecular masses. SEC also clearly distinguished laccase from tyrosinase, another abundant cell wall oxidase in the Peltigerineae. Most species contained one oligomeric laccase isoform. Analysis of replicate collections of four species from different localities showed the isoform a given species contains does not vary with geographical location. The absorption spectra of lichen leachates suggested lichen laccases sometimes resemble the “yellow” laccases found in some free-living fungi. The thermostabilities of lichen laccases were only moderate; most of their activity remained after several hours at 40°C, but at 50°C activity was rapidly lost. Results indicate that considerable diversity in laccase isoforms exists in lichens.