A species of Verticillium (strain TM-759), an imperfect fungus isolated from a basidiocarp of Coltricia cinnamomea, produces three new antibiotics, verticillins A (Ia), B (XVIII), and C. Antimicrobial activity has been found against Gram-positive bacteria and mycobacteria but not against Gram-negative bacteria and fungi. The cytotoxicity effects (EDm) of verticillins A and B against HeLa cells were both 0.2 μg ml⁻¹. Stereostructures of verticillins A and B, which are derivatives of bi-(3,11a-epidithio-1,4-dioxopyrazino[1',2':1,5]pyrrolo[2,3-b]indol-10b-yl), have been elucidated by chemical and physicochemical methods. Verticillin C is thought to be an epitrithio-analogue of verticillin B.