Desoxyhemigossypol (dHG), a phytoalexin produced by cotton in response to infection has been shown to be highly toxic to the pathogen, Verticillium dahliae, soluble in water at the pH of infected xylem vessels at concentration higher than those required to kill conidia and mycellia, and present in vivo at the site of infection and in contact with the mycellia. However, the structure-activity of this compound is unknown. Recent evidence suggests dHG readily forms a free radical by autoxidation, which can be initiated by trace quantities of transition metals such as iron. Reducing agents that stabilize dHG have been shown to significantly reduce it a toxicity to V. dahliae. Thus, the dHG free radical is implicated as an essential element in the mechanism of fungitoxicity.