Pyrrocidine B is a rare 13-membered macrocyclic antibiotic produced by an unidentified fungus, LL-Cyan426, by Carter and co-workers at Wyeth-Ayerst in 2002. In 2008 Wicklow and Poling, USDA, subsequently identified the same metabolite from the plant pathogen, Acremonium zeae. Pyrrocidine B is active against Gram positive bacteria and yeast, albeit less potent than pyrrocidine A. Pyrrocidines A and B are potently active against fungi infesting cereal crops, including Fusarium graminearum, Nigrospora oryzae, Stenocarpella (Diplodia) maydis, Rhizoctonia zeae and Clavibacter michiganense subsp. Nebraskense, the causal agent of Goss’s bacterial wilt of maize. Pyrrocidines A and B have been identified as key active principals of Acremonium zeae, a protective endophyte of maize. Pyrrocidines A and B are also inducers of apoptosis in HL-60 cells.