Abstract An immobilised whole cell Rhodococcus sp. (SP 361) has been shown to be an effective catalyst for the stereoselective hydrolysis of both racemic and prochiral nitrile containing compounds. 2-Alkyl-arylacetonitriles 6a- 8a were hydrolysed to ( S)-acids and ( R)amides whereas the closely related substrate 9a gave the ( R)-acid. A series of prochiral dinitriles 10a- 13a were hydrolysed to the corresponding ( S)-acids with e.e.'s 22–84%. Models to account for the stereoselectivity of the enzymic hydrolyses have been proposed.