USF-19A, a soybean lipoxygenase (SBL) and human 5-lipoxygenase (5-LO) inhibitor, was isolated from Streptomyces sp. USF-19 strain. Its chemical structure was determined by spectroscopic evidence to be a new member of the antimycin antibiotic family. The IC50 value of USF-19A against 5-LO was 28.0 microM.