A novel platelet activating factor (PAF) antagonist, Sch 47918, was isolated from the fermentation broth of the fungus, Phoma sp. The structure of this compound was elucidated by spectroscopic methods. The proposed structure and stereochemistry of Sch 47918 were confirmed by single-crystal X-ray diffraction analysis. Sch 47918 was found to be active at IC50 = 6.96 muM in the in vitro PAF-induced human platelet aggregation assay.