The second step in aromatic hydrocarbon biodegradation pathway is catalyzed by the activity of a dihydroxy-di-hidrodiol dehydrogenase (DHD) enzyme that uses NAD as cofactor. There exist only few reports about this enzyme in filamentous fungus. Previously, we were capable to detect an activity band using electrophoretic zymograms revealed with phenanthrene-diol as substrate. In this work, we are interested in the detection and characterization of naphthalene diol-dehydrogenases that could be the enzymes that catalyze the second step in the aromatic hydrocarbon biodegradation pathway. The results suggest the presence of different DHD activities depending of the cofactor NAD or NADP used in the mixture to reveal the enzymatic activity.