A rapid, sensitive and selective method using LC-MS/MS was developed and validated for the simultaneous quantitative determination of five polyamines N1,N12-diethylspermine (DESpm), N-ethylspermine (EtSpm), N1-ethylspermidine (EtSpd), spermidine (Spd) and N1-ethyl-1,3-diaminopropane (EtDAP) without any derivatization steps. The LC-MS/MS system was operated using the positive electrospray ionization (ESI) mode. The chromatographic separation only took 10min and was performed on a reversed phase C18 column with 0.1% heptafluorobutyric acid as the ion-pairing agent and acetonitrile gradient. Stable, deuterium labelled internal reference compounds of the five analytes were included in the quantification. The lower limit of quantification for all of the five analytes was 0.03microM and the method was linear for DESpm, EtSpd, Spd and EtDAP over the range of 0.03-60microM and for EtSpm over the range of 0.03-30microM. Correlation coefficients (R2) were always >0.995 for all the analytes. The precision of the overall method ranged from 0.2 to 9.7% as intra-day variability and from 0.9 to 6.8% as inter-day variability. The intra-day and inter-day accuracy of the assay ranged between 87.6-109.8% and 89.6-106.6%, respectively. The method has been applied successfully to quantify metabolites of DESpm as a substrate for recombinant human polyamine oxidase.