The presence of clamp connections on hyphae and the development of fruiting bodies in culture are primary characters which allow identification of the basidiomycete Schizophyllum commune in cases of human infection. The diagnostic problems presented by a nonclamped, nonfruiting isolate from a dense mass in the right upper lobe of the lung in a female with a past history of pulmonary tuberculosis and diabetes are described. Several features of the isolated fungus, including rapid growth rate and white, dense, cottony colonies, tolerance to the fungicide benomyl at a concentration of 10 micrograms/ml, and susceptibility to cycloheximide at 400 micrograms/ml, suggested that it might be a basidiomycete. Transmission electron microscopy showed the presence of a dolipore septum with perforate pore cap characteristic of fungi in the class Holobasidiomycetes. However, species identification remained elusive until compatibility tests with known single-basidiospore isolates confirmed the identification of the sterile lung isolate as S. commune. Sequence analysis of the 5' internal transcribed spacer region of ribosomal DNA further supported conspecificity.
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