The cyclohexanone monooxygenase (CHMO) gene of Acinetobacter sp. NCIMB 9871 was simultaneously expressed with the genes encoding molecular chaperones and foldases in Escherichia coli. While the expression of the CHMO gene alone resulted in the formation of inclusion bodies, coexpression of the chaperone or foldase genes remarkably increased the production of soluble CHMO enzyme in recombinant E. coli. Furthermore, it was found that molecular chaperones were more beneficial than foldases for enhancing active CHMO enzyme production. The recombinant E. coli strain simultaneously expressing the genes for CHMO, GroEL/GroES and DnaK/DnaJ/GrpE showed a specific CHMO activity of 111 units g(-1) cell protein, corresponding to a 38-fold enhancement in CHMO activity compared with the control E. coli strain expressing the CHMO gene alone.