Twenty-eight cultures of ectomycorrhizal fungi isolated from diverse host and habitat associations were tested in pure culture syntheses with the ericaceous hosts Arbutus menziesii Pursh and Arctostaphylos uva-ursi (L.) Spreng. All but three of the fungi formed arbutoid mycorrhizas. Sheathing fungal mantles, Hartig net penetration and intracellular colonization were well developed on most mycorrhizas. These results confirm that ectomycorrhizal fungi form arbutoid mycorrhizas and that these particular hosts are broadly receptive towards fungal associates. The significance of these results with respect to ecological and practical implications and better understanding of ectomycorrhizal specificity is emphasized. Arbutoid mycorrhizas are most closely related to ectomycorrhizas than to ericoid mycorrhizas.