A polycyclic aromatic hydrocarbon degrading Mycobacterium gilvum, strain LB307T, was able to degrade the azaarenes 5,6-benzoquinoline, 7,8-benzoquinoline, and phenanthridine (nitrogen-containing heterocyclic aromatic hydrocarbons) under aerobic conditions. The strain was able to use 5,6-benzoquinoline as sole sources of carbon, nitrogen, and energy. However, inhibition of degradation and growth was observed with increasing substrate concentration. During degradation, metabolites built up transiently. One of the metabolites detected during 5,6-benzoquinoline degradation is suggested to be 2-oxo-5,6-benzoquinoline. This is the first report on bacterial degradation of phenanthrene-analogue azaarenes.