Abstract(S)-p-Hydroxy-mandelonitrile lyase from Sorghum bicolor has been crystallized in three different forms using the hangingdrop vapor-diffusion technique. Crystal tbrm I is obtained from 1.4M (NH4)2SO 4 in 100mM Na-acetate, pH 4.6, and belongs to the orthorhombic space group P2~2t2 ~. The cell dimensions are a = 71.4, b = 95.8, c = 149.1 A. A complete set of diffraction data has been collected to 2.6 A resolution. Form II crystals are grown from 500mM Li2SO 4 in 13% polyethylene glycol 8000. These crystals appear as hexagonal plates and diffract to 2.98]k resolution but apparently are twinned. Cocrystallizing hydroxynitrile lyase with the inhibitor benzoic acid using 1.4M (NH4)2SO 4 in 100mM Na citrate, pH 5.4 as precipitant yields crystal form III, which belongs to the monoclinic space group C2 with a = 150.7, b= 103.7, c=90.6A, fl= 101.3. X-ray diffraction data were collected to 2.3 A resolution.