In various bacterial strains belonging to the β-subdivision of proteobacteria which are capable of degrading chlorinated monoaromatic compounds, chlorocatechol 1,2-dioxygenase genes were detected by PCR and Southern hybridization. Using PCR primers derived from the conserved sequence motifs of chlorocatechol 1,2-dioxygenase genes tfdC, clcA and tcbC, PCR products of the expected size were obtained with the test strains, but not with negative control strains. The specificity of the PCR products was verified by hybridization using an oligonucleotide probe for an internal sequence motif which is evolutionarily conserved among chlorocatechol 1,2-dioxygenases and some other dioxygenases that catalyze the intradiol aromatic-ring-cleavage. Hybridization with the tfdC PCR product from the 2,4-D degradative plasmid pJP4 under stringent conditions revealed different extents of homology of the chlorocatechol 1,2-dioxygenase genes to the canonical tfdC sequence in the various strains. These findings were confirmed by the nucleotide sequence analysis of the tfdC-specific PCR products. From our results, we conclude that the PCR primer set is more suitable than the hybridization with pJP4-derived gene probes for the detection of diverse chlorocatechol 1,2-dioxygenase genes in proteobacteria.