Some enzymes, particularly esterases and phosphatases, are commonly variable within lichen populations. Mycobiont cultures of Cladonia cristatella Tuck, were examined electrophoretically in order to determine whether isozymes of these enzymes varied among 12 cultures initiated from single ascospores of the same apothecium. There were significant differences among mycobionts with respect to growth in liquid malt-yeast medium, and there was isozymic variability among them just as there is among intact thalli in natural lichen populations. These results are consistent with the idea that in nature ascospores could participate in the reproductive process. Enzymatic differences within a population may originate from propagules, including sexual ones, which initiate individual thalli.