On gas chromatographic analysis, N-(5-pyrrolidinopent-3-ynyl)succinimide N'-oxide gave rise to three main decomposition products, which were assigned the structures N-(3-oxopent-4-enyl)succinimide, N-(penta-3, 4-dienyl)succinimide and N-3(3-pyrrolidino-3-oxopropyl)succinimide. These three products were identified by electron impact mass spectrometry, using deuterium substituted N-oxides, and mechanisms for the formation of the former two are proposed. By gas chromatographic mass spectrometric analysis, extracts from metabolic incubation of N-(5-pyrrolidinopent-3-ynyl)succinimide were shown to contain the N-oxide, as previously indicated by indirect methods.