The influence of a stereocenter already present in the molecule on the selectivity displayed by almond oxynitrilase has been addressed, considering the substituted aldehydes (+/-)-2-phenylpropionaldehyde 1 and (+/-)-3-phenylbutyraldehyde 2 as model substrates. Only when the stereocenter was adjacent to the aldehyde group (as in 1) a strong influence on the selectivity of this enzyme was observed, resulting in the formation of the four possible cyanohydrins although in different ratio. On the other hand, the cyanohydrins obtained from 2 had the expected 2R configuration. Copyright (C) 1996 Elsevier Science Ltd