The scope of the biotransformation of a series of azaarene compounds by recombinant whole-cells of Escherichia coli JM109(DE3)(pDTG141) expressing the naphthalene dioxygenase system (NDOS) from Pseudomonas sp. NCIB 9616-4 was explored. The present study establishes that several bicyclic azaarenes are good substrates in the NDO-catalysed reaction, giving cis-dihydrodiol derivatives; monohydroxylated products were also observed.