Ali Khan, Hall and Robinson1 have reported that when a Gram-negative bacterium (probably Pseudomonas sp.) was grown in an aqueous suspension of n-octane plus mineral salts, dioic acids (mainly suberic acid) were recovered from the medium. The activity of this bacterium (culture kindly presented by Dr. A. N. Hall) and of ten other species of bacteria on cyclic ketones has been investigated. There appears to be no previous report of microbiological oxidation of cyclic ketones. In his limited survey, Baldacci2 could not detect any microbial activity on Cyclohexanone.