Juglone (5-hydroxynaphthoquinone) is a pigment found in several plant species, notably in the genus Juglans (walnuts and pecans) and has been reported as a metabolite of the plant pathogenic fungus, Verticillium dahlia. Juglone exhibits allelopathic, antifungal, herbicidal and anti-tumor activities and has been shown to induce quinone reductase and glutathionone transferase. Juglone is a useful standard for analytical and bioassay dereplication of crude microbial extracts.