alpah-Hydroxy alkanones were synthesised with high enantiomeric purity by stereoselective enzyme-catalysed diketone reduction. Both diketone reduction and cofactor regeneration were accomplished with purified carbonyl reductase from Candida parapsilosis (CPCR2). The reaction products were isolated by column chromatography and analysed by chiral GC measurements, 1H-NMR spectroscopy and determination of optical rotations. Preparative-scale biotransformations yielded 350–600 mg of pure aliphatic alpha-hydroxy ketones including the difficult to obtain (S)-2-hydroxypentane-3-one. For all the products good enantiomeric excesses in the range of 89–93% were achieved.