<jats:p> Culture filtrates of Nectria radicicola Gerlach & Nilsson yielded two products: a peptide fraction, "radicicolin", and a phenolic substance, radicicol (monorden), C18H17ClO6. Chemical and spectroscopic studies showed that radicicol was a macrolide with structure (Ia). Brefeldin A was isolated from filtrates of other strains of the organism.