Cyclohexanone monooxygenase (CHMO) from Acinetobacter sp NCIMB 9871 expressed in baker's yeast and in E. coli and cyclopentanone monooxygenase (CPMO) from Comamonas (previously Pseudomonas) sp. NCIMB 9872 expressed in E. coli are new bioreagents for Baeyer-Villiger oxidations. These engineered microorganisms, requiring neither biochemical expertise nor equipment beyond that found in chemical laboratories, were evaluated as reagents for Baeyer-Villiger oxidations of cyclopentanones substituted at the 2-position with polar and nonpolar chains suitable for further modifications. Two such functionalized substrates that can be transformed into highly enantiopure lactones were identified. The performance and the potential of these bioreagents are discussed.Key words: enantioselective Baeyer-Villiger oxidations, biotransformations, cyclohexanone monooxygenase, cyclo pentanone monooxygenase, engineered baker's yeast, recombinant E. coli, optically pure 2-substituted cyclopentanones, optically pure lactones.