Crystalline coenzyme Q 10 has been newly isolated from a fermentation using Pseudomonas denitrificans. Previously, the presence of Q 9 in Pseudomonas fluorescens, and Q 10 in Neurospora crassa and in Chromatium was reported by others, but without evidence based on characterization of isolated crystalline material. We found Q 9 in five other species of Pseudomonas, Q 8 and Q 9 in Pseudomonas fluorescens, and evidence for the presence of some form of Q in 32 cultures, representing 20 species out of 107 cultures which were examined. Coenzyme Q 10 can now be produced by a suitable fermentation, rather than by isolation from mammalian tissue.