A simple and rapid spectrophotometric method, based upon the UV absorption of NADH, for the measurement of putrescine by the combined use of aminobutyraldehyde dehydrogenase (EC 1.2.1.19) and putrescine oxidase (EC 1.4.3.10) was established. Simplified purification procedures for the analytical use of aminobutyraldehyde dehydrogenase of Pseudomonas putida and putrescine oxidase of a newly isolated Gram-positive soil bacterium were developed. When aminobutyraldehyde dehydrogenase alone was used, the amount of 4-aminobutyraldehyde and the absorbance of NADH formed during the enzyme reaction had a precisely linear relationship in the range from 2 to 80 nmol of 4-aminobutyraldehyde. A comparable accuracy and sensitivity was obtained when a combination of putrescine oxidase and aminobutyraldehyde dehydrogenase was used to measure putrescine.