Diketopiperazines, Sch 54794 and Sch 54796, have been isofated from a fungal fermentation. The structures of these compounds have been established based on spectroscopic data analysis. Sch 54794 exhibited inhibitory activity in the platelet activatingfictor (PAF) assay. In the course of searching for bioactive substances from fungal fermentations,lt2 we have isolated two new compounds, Sch 54794 (1) and Sch 54796 (2), from the fermentation of a fungal culture, ToJypocJadium sp. The microorganism, ToJypocJadium sp., was isolated from dead twigs from a Quercus virginiana Miller, an old live oak tree in the state of Tamalupas, Mexico.3 The structures of 1 and 2 were determined as cis and tram isomers by analysis of the spectroscopic data. This paper details the bioassay-guided isolation and structure elucidation.