Hemigossypol (HG), methoxyhemigossypol (MHG), desoxyhemigossypol (dMHG) and desoxymetoxyhemigossypol (dMHG) from Verticillium dahliae-infected, wilt-resistant Seabrook Sea Island-(SBSI) cotton were tested at pH 6.3.-7.5 in liquid nutrient media for toxicity to V. dahliae. The terperioids dHG, HG, dMHG, and MHG killed conidia at 10, 45, 25 , and 60 µg/ml, respectively; and mycelia after 48 hr at 15, 35, 25, and 45 µ/ml, respectively. Only dHG was sufficiently water soluble at pH 6.3 (maximum pH of infected xylem) to account for death of V. dahliae conidia and mycelia at most sites in the stem stele 10 days after inoculation. The dHG in the stem stele was well in excess of fungicidal concentrations at 10 days after inoculation. Desoxyhemigossypol, the precursor of HG, reacted with the SbCl₃ reagent to give a green-colored Sb-dHG product, specific for dHG(3) in the same specialized paravascular parenchyma cells of diseased stem stele which contain HG.