A new intermediate in the biosynthesis of the benzo[b]fluorene antibiotic, kinamycin D, has been identified. 11-Amino-4,5,9-trihydroxy-2-methyl-10H-benzo[b]fluoren-10-one was synthesized and shown to be present in extracts of Streptomyces murayamaensis fermentations. A deuterated sample was prepared and shown to be specifically incorporated into kinamycin D. This new intermediate, now named stealthin C, is also the probable hydroxylation substrate for the biosynthesis of stealthin A by S. viridochromogenes.