Abstract: The present invention relates to a method for producing a product of a reaction catalysed by a nitrilase, which method comprises the steps (i) providing a microorganism comprising said nitrilase located on its surface, and/or a membrane preparation of said microorganism, and (ii) contacting the microorganism and/or the membrane preparation thereof with one or more nitrilase substrates under conditions compatible with nitrilase activity. The present invention further relates to a method for producing enantiomerically pure (R)-mandelic acid using the nitrilase-displaying whole cell biocatalyst or membrane preparation thereof for the conversion of racemic mandelonitrile.