Residual acrylonitrile monomer was quantitatively removed from aqueous polymer emulsions (latexes) of nitrilic rubbers by means of whole cells and cellular lysates of Brevibacterium imperiale and Corynebacterium nitrilophilus. A commercially-available immobilized nitrilase preparation allowed the conversion of acrylonitrile into acrylic acid and the recycle of the catalyst with retention of the reaction efficiency.