Monocerin, an antifungal metabolite of Helminthosporium monoceras, is shown to be 2,3,3a,9b-tetrahydro-6-hydroxy-7,8-dimethoxy-2-n-propyl-5H-furo[3,2-c][2]benzopyran-5-one (Ia). Structures are also assigned to three related metabolites—hydroxymonocerin (Id), monocerone (Ie), and monocerolide (V).