The synthesis of the aroma chemical cinnamyl alcohol (CMO) by means of enzymatic reduction of cinnamaldehyde (CMA) was investigated using NADH-dependent alcohol dehydrogenase from Bacillus stearothermophilus both as an isolated enzyme, and in recombinant Escherichia coli whole cells. The influence of parameters such as reaction time and cofactor, substrate, co-substrate 2-propanol and biocatalyst concentrations on the bioreduction reaction was investigated and an efficient and sustainable one-phase system developed. The reduction of CMA (0.5 g/L, 3.8 mmol/L) by the isolated enzyme occurred in 3 h at 50 A degrees C with 97 % conversion, and yielded high purity CMO (a parts per thousand yen98 %) with a yield of 88 % and a productivity of 50 g/g(enzyme). The reduction of 12.5 g/L (94 mmol/L) CMA by whole cells in 6 h, at 37 A degrees C and no requirement of external cofactor occurred with 97 % conversion, 82 % yield of 98 % pure alcohol and a productivity of 34 mg/g(wet cell weight). The results demonstrate the microbial system as a practical and efficient method for larger-scale synthesis of CMO.