An antibody directed toward putrescine has been produced in rabbits by immunization with a putrescine-protein conjugate which was prepared by a procedure of coupling putrescine to mercaptosuccinylated bovine serum albumin using N-(γ-maleimidobutyryloxy)succinimide as a coupling agent. In the analysis of ouchterloney double immunodiffusion, anti-putrescine serum produced precipitation line with BSA-putrescine, but not with BSA. Anti-putrescine serum showed 5.3% crossreaction with cadaverine, 3.5% with spermine, and 2.3% with sper-midine but not crossreactions with 1,3-diaminopropane and lysine. An radioimmunoassay for putrescine has been developed utilizing anti-putrescine serum bound to nitrocellulose and [1,4-^(14)C]putrescine. The lower limit of detection by this assay was 100 p㏖/tube. In the correlation studies of putrescine determined by this methods (RIA, HPLC, TLC method), RIA showed good correlation with other two methods. This RIA method was turned out to be reproducible, specific, accurate, rapid and simple for determination of putrescine without making derivative of putrescine.