The addition of a small quantity of glucose (0.5 g 1−1) to the culture medium enhanced mycorrhiza formation on Vaccinium angustifolium Ait. and V. corymbosum L. with Pezizella ericae Read in vitro. Under these conditions, 15 isolates of ericoid mycorrhizal fungi obtained from diverse hosts and habitats demonstrated different abilities to colonize the root system of the two species of Vaccinium. Moreover, the addition of activated charcoal especially in presence of glucose or pectin greatly stimulated ericoid mycorrhiza formation by P. ericae on V. angustifolium. The possibility that active charcoal adsorbs toxic compounds from the rhizosphere is discussed.