Methylhydroquinone is an intermediate in the degradation of fenitrothion by Burkholderia sp. NF100. The catabolic gene (mhq) for methylhydroquinone degradation encoded on the plasmid pNF1 in the strain was cloned and sequenced. The mhq clone contained two ORFs, mhqA and mhqB, of which the deduced amino acid sequence shared significant homology with NAD(P)H-dependent flavoprotein monooxygenases and extradiol dioxygenases, respectively. Parts of the consensus sequences of the monooxygenase gene and dioxygenase gene have been identified in MhqA and MhqB from strain NF100, respectively. MhqA was overexpressed in Escherichia coli, and partially purified MhqA catalyzed the NADPH-dependent hydroxylation of methylhydroquinone. MhqB was also overexpressed in E. coli, and the purified enzyme showed an extradiol ring cleavage activity toward 3-methyleatechol but a very low activity was observed toward 4-methylcatechol.