The most abundant metabolite of the eucalyptus leaf spot pathogen Mycosphaerella cryptica was extracted from agar cultures. The structure of the compound was elucidated by detailed studies of NMR and MS data and by comparison with derivatives. The compound is a previously undescribed diphenylether structurally related to pannaric acid found in lichens. Culture extracts from another species of Mycosphaerella isolated from the same environment yielded 5-hydroxymethylfuran-3-carboxylic acid, a furan acidic compound previously isolated from a basidiomycete fungus. Assays for bioactivity of these metabolites revealed no evidence for antimicrobial activity. Some phytotoxicity was seen on newly emerged leaves of Eucalyptus globulus, but not on juvenile or adult leaves, when treated with either metabolite.