A new series of naphthoquinones has been isolated from a member of the Streptomyces group. This series contains five quinones which vary from each other in the degree of unsaturation of their C3 isoprenoid side chain. By thin-layer chromatography, ultraviolet, infrared, and nuclear magnetic resonance spectra, and mass spectroscopy these quinones have been identified as MK9, MK9(2-H), MK9- (4-H), MK9(6-H), and MK9(8-H). © 1969, American Chemical Society. All rights reserved.