Several Baeyer-Villiger monooxygenases converting a wide spectrum of substrates have been discovered, cloned, and characterized throughout the last few years. Still, only a few of them are applicable for large-scale conversion predominantly due to their sensitivity towards high substrate and/or product concentrations. The recently cloned and characterized 4-hydroxyacetophenone monooxygenase from Pseudomonas putida JD1 shows excellent enantioselectivity towards 3-phenyl-2-butanone with E > 100 but is inhibited by concentrations > 10 mM of both substrate and product. This obstacle could be circumvented by in situ substrate feed and product removal using a hydrophobic LewatitA (R) adsorbent resin. Thus, the concentration of 3-phenyl-2-butanone could be increased from 1.4 to > 26 mM without significant reduction in conversion.