In this paper, we compared the chemical and biological activities of natural and synthetic clavamines, N-[2,4-dihydroxyphenylacetyl-4-L-asparaginyl)-N'-[N-(L-arginyl-glycyl-L-alanyl)-8-amino-4-azaoctanoyl]-1,5-pentanediamine (DPA->Asn->Cad<--Ptr<--Ala<--Gly<--Arg) [DPA, 2,4-dihydroxyphenylacetic acid; Cad, 1.5-pentanediamine (cadaverine); Ptr, 8-amino-4-azaoctanoic acid (putreanine, or carboxyethylputrescine)], and found that both were identical. Both compounds showed the same Rf value in thin-layer chromatography and the same retention time in high performance liquid chromatography (HPLC). Both hydrolyzates consisted of the same components, such as Gly, DPA, Ala, Asp, Arg and Ptr in gas chromatography. The Edman degradation of both compounds also gave exactly the same sequence. The 1H-NMR spectrum and fast atom bombardment (FAB) mass spectrum of the synthetic compound coincided with those of the natural one. Both were active on the insects used. Clavamine was the main component of the insecticidal activity in the crude venom. By this synthetic study, the structure of a new venom insecticide was thus established. The synthetic compound in abundant quantity will be advantageous for practical use as an insecticide over natural ones, because the latter is available only in small amounts. Also, it will be useful for the exploitation of a new field of biochemistry for polyamines.