Single crystals of three different isoenzymes of (R)-(+) mandelonitrile lyase (hydroxynitrile lyase) from almonds (Prunus amygdalus) have been obtained by hanging drop vapor diffusion using polyethylene glycol 4000 and isopropanol as co-precipitants. The crystals belong to the monoclinic space group P2(1) with unit cell parameters a = 69.9, b = 95.1, c = 95.6 A, and beta = 118.5 degrees. A complete set of diffraction data has been collected to 2.6 A resolution on native crystals of isoenzyme III.