This brief article is dedicated to the late Professor Morizo Ishidate, and concerned in a methodology developed by the author and collaborators, aiming at the regulation of polyamine, especially, the regulation of spermidine synthase. The content is separated in 3 sections. The first section on the development of analytical methods, contains seven items, e.g. fluorometric determination of polyamines by fluorescamine, analysis of naturally occurring polyamines by GC and GC-MS, etc. The second section on the syntheses of needed compounds, contains three items, e.g. syntheses of decarboxylated S-adenosylmethionine which is a substrate for spermidine synthase and its related compounds, syntheses of ¹5N-enriched polyamines applicable to the preparation of various polyamines, etc. The last section on the studies of aminopropyl transferases, contains three items, e.g. purification of spermidine synthase from mammalian tissues using ATPA-Sepharose, a novel affinity carrier, newly developed inhibitors for the enzymes, etc.