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Agmatine iminohydrolase (EC 3.5.3.12) was purified 7,300-fold from extracts of corn shoots by chromatographic separations on diethylaminoethyl-celulose, Sephadex G-100, and agmatine-affinity column. The enzyme was homogeneous by the criteria of analytical gel electrophoresis. Molecular weight estimated by Bio-Gel P-200 was 85,000, and the enzyme seems to be a dimer with identical subunits (molecular weight, 43,000). The isoelectric point determined by gel electrofocusing was 4.7. The optimal pH and temperature for activity were 6.5 and 60 C, respectively. The activation energy was 10.9 kilocalories per mole. High specificity exists for agmatine, the Km value for agmatine was 1.9 x 10-molar, and the enzyme was present in the cytosol. The enzyme was sensitive to Cu2" and Zn21 and also was inhibited by p-hydroxymercuribenzoate and arcain.Putrescine in some higher plants seems to be formed via NCP' (15,20). The discovery of agmatine iminohydrolase in corn, sunflower (14), and groundnut (13) provided a priori evidence for enzymic formation of NCP from agmatine. Agmatine iminohydrolase catalyzes the hydrolysis of agmatine to NCP and ammonia as follows: agmatine + H20 -NCP + NH3 Although the enzyme has been purified (about 375-fold) from groundnut cotyledons (13), no attempts seem to have been made so far to obtain the enzyme in homogeneous form from corn or any other plant source. We report here a procedure for the purification of agmatine iminohydrolase from corn shoots and describe the enzyme properties.