Escherichia coli recombinants expressing xylene oxygenase (XO) from the TOL plasmid pWWO of Pseudomonas putida mt-2 were used in two-liquid phase fermentations with n-octane as a semi-inert second liquid phase, to produce epoxides derived from styrene. The toxicity of styrene in a two-phase system was significantly reduced as compared to single-phase fermentations. Styrene, 3-chlorostyrene, and 4-chlorostyrene were efficiently oxidized by the biocatalyst yielding optically active epoxides with enantiomeric excesses of 92%, 96%, and 37% respectively 3-Methylstyrene and 4-methylstyrene, however, were primarily oxidized at the methyl moiety rather than the vinyl group, thus resulting in the formation of 3-vinylbenzylalcohol and 4-vinylbenzylalcohol. Small amounts of 3-methyl-and 4-methylstyrene epoxide were formed here also. These products were produced at an estimated enantiomeric excess of over 95%.