While examining azalea galls for the presence of fungi that may produce plant growth regulators, we isolated Trichoderma harzianum in a pure culture, fermented it on solid media, and examined the crude extract for biologically active natural products. As a result of a bioassay-directed isolation, the secondary metabolite, (-)-harzianopyridone (Fig. 1), was found in sufficient quantity to be evaluated in greenhouse-grown bean, corn and tobacco plants, and in disk assays against Gram-positive and negative bacteria, and fungi. Earlier, this compound had been isolated from T. harzianum as a racemic mixture, but was not examined for biological activity, except for its antifungal properties. We now report some of the biological properties of a laevorotatory sample, of unknown optical purity, of harzianopyridone.