An alliin lyase (EC 4.4.1.4) preparation from garlic, Allium sativum L., has been purified to apparent homogeneity. The purification procedure involved liquid chromatography steps on hydroxylapatite, on an anion exchanger, and on a chromatofocussing medium. The enzyme protein was characterized by a relative molecular mass of 108,000, and was found to consist of two equal subunits. Its isoelectric point was determined to be 4.9. The enzyme appeared rather thermolabile. Simulated gastric-intestinal passage by a modified “half change test” revealed a high acid lability of the active alliinase protein. Km-values for different substrates were in the mM range, and activating energies for the cleavage of different substrates could be determined. A maximal specific activity for synthetic alliin in the range of 490 µmoles per min and mg protein could be achieved at 33 °C. There are some significant differences in the characterization of the purified protein compared to results previously reported by others on this enzyme.