Fluoro-labelled substrates and membrane inlet mass spectrometry (MIMS) was used to test the bioconversion potential of the white-rot fungus Bjerkandera adusta with respect to a production of novel halogenated aromatic compounds. The presence of a fluorine atom on the aromatic ring of possible precursors to the well-known metabolites, 3-chloro-4-methoxybenzaldehyde and 3,5-dichloro-4-methoxybenzaldehyde, did not influence the metabolism and they all gave mixed chloro-fluoro-methoxybenzaldehydes; however, we were unable to produce any new chlorinated compounds. Neither supplementation of anisole, benzaldehyde, veratryl alcohol, the naphthalene analogs nor methyl-substituted benzaldehydes resulted in a production of detectable amounts of the corresponding chlorinated products. Apparently, only hydroxybenzaldehydes and/or methoxybenzaldehydes are chlorinated by the halogenating system. Experiments where an aromatic alcohol, aldehyde, or the analog acid was supplemented gave qualitatively and quantitatively similar membrane inlet mass spectra suggesting that oxidases and reductases maintain a stoichiometric ration between these compounds. Several cases of hydroxylation and/or methoxylation of the substrates were also observed.