A novel metabolite, auranthine, has been isolated from sporing cultures of Penicillium aurantiogriseum and its structure, 6,7,7a,8-tetra hydroquinazolino [3',2':1,6] pyrido [2,3-6] [ 1,4] benzodiazepine-9,16 dione comprising anthranilate and glutamine moieties, has been elucidated from spectral evidence and biosynthetic reasoning. In the course of isolating and characterising nephrotoxic and other metabolites from a fungus which was originally described as P. uerrucosum var. cyclopium but which is now assigned as P. aurantiogriseum,2 a new alkaloid has been found. Acetone extracts of lyophilised whole fungal cultures were resolved by column chromatography and semi-preparative reversed-phase h.p.1.c. A prominent component (2 mg/100 ml culture) was isolated and for which the name auranthine and structure (1) are proposed.