The structure of versimide, a metabolite of Aspergillus versicolor, has been established as methyl (+)-(R)-α-(methylsuccinimido)acrylate. Aspergillus versicolor is noted for producing complex xanthones, anthraquinones, and a γ-pyrone. Examination of a strain of A. versicolor led to the isolation of a new optically active liquid metabolite, C₉H₁₁NO₄, herein called versimide. Structural determination involved n.m.r. spectroscopy, catalytic reduction to form dihydroversimide, hydrolysis (yielding alanine hydrochloride and (R)-methylsuccinic acid), i.r. spectroscopy, and synthesis of racemic α-(methylsuccinimido)propionic acid and its methyl ester, confirming versimide's structure. The only other reported naturally occurring imide is pencolide, an acid isolated from Penicillium multicolor.