Reactions of pea diamine oxidase (PSAO) and maize polyamine oxidase (MPAO) with 1,4-bis(3-aminopropyl)-piperazine (BAPP), diethylenetriamine (DETA), dipropylenetriamine (DPTA), dehydrospermine (DHSP) and 3-oxapentane-1,5-diamine (OPD) were studied and compared. These reactions were characterised by kinetic measurements (kinetic constants, stoichiometry) and by measurements of absorption spectra (reaction mechanisms). In the case of oxidised polyamine compounds, the corresponding reaction products were determined using analytical methods (coloured trapping reactions, mass spectrometry, IR spectroscopy, thin layer chromatography). Some of the compounds were found to be substrates of PSAO and relatively potent inhibitors of MPAO (and vice versa) all at once. The others showed the same effect on both enzymes. This may have an importance for designing of experiments in physiological studies in plants.