Two strains, using 6-hydroxyquinoline as sole source of energy, carbon and nitrogen, have been isolated. These bacteria, designated 31/1 Fa1 and 31/2 A1, are also able to degrade quinoline. According to their physiological properties strain 31/1 Fa1 has been identified as Pseudomonas diminuta and strain 31/2 A1 as Bacillus circulans. 6-Hydroxy-2-oxo-1,2-dihydroquinoline was found as intermediate in the degradation of 6-hydroxyquinoline and quinoline. 2-Oxo-1,2-dihydroquinoline was the first metabolite in the degradation of quinoline.