Pseudomonas azelaica HBP 1 contains a 2-hydroxybiphenyl 3-monooxygenase (E.C. 1.14.13.44, HbpA) which produces 3-substituted catechols from 2-substituted phenols. The tetrameric enzyme (subunit mass 60 kDa) carries FAD as a prosthetic group, uses NADH as cofactor and is homologous to a number of NADPH dependent flavin containing phenol monooxygenases. HbpA regio-selectively oxidizes 2-substituted phenols and has a broad substrate-range. As ortho-substituent it accepts various alkyl-residues, halogen atoms and substituted phenyl-residues. We have used this monooxygenase for the production of 3-substituted catechols, which are useful synthons that are difficult to obtain by chemical means. A recombinant E. coli JM101, containing the hbpA gene, was used for whole-cell biotransformations. Since the phenols as well as the corresponding catechols produced are toxic to cells, a process with a limited feed of starting-material combined with in situ product recovery was used. 3-Phenyl-, 3-chloro-, 3-bromo-, 3-ethyl-, 3-propyl-, 3- i-propyl-, and 3- sec-butyl-catechol could thus be produced in gram amounts with space-time yields up to 0.45 g l −1h −1. The products were recovered and further purified by recrystallization. Authenticity of all products, some of which had not been described before, was verified by 1 H NMR, 13 C NMR, IR spectroscopy and GC/MS.