Thirty-five strains of soil bacteria were grown with biphenyl (BP) and tested for their capacity to cooxidize dibenzofuran (131317). During metabolism of DBF, the culture medium of 17 strains changed from colorless to orange, indicating a meta-cleavage pathway of DBF degradation. The ring cleavage product of these isolates was shown to be 2-hydroxy-4-(3'-oxo-3'H-benzofuran-2-yliden)but-2-enoic acid (HOBB). The strain SBUG 271, studied in detail and identified as Rhodococcus erythropolis, degraded DBF via 1,2-dihydroxydibenzofuran. The ensuing meta-cleavage yielded HOBB and salicylic acid, In addition, the four monohydroxylated monomers of DBF and two metabolites. which were not further characterized, were detected. Thus. our results demonstrate that the metabolic mechanism involves lateral dioxygenation of DBF followed by meta-cleavage and occurs in Gram-negative as well as in Gram-positive BP-degrading bacteria.