The objective of this study was the development and the evaluation of competitive ELISA assays based on monoclonal antibodies for the detection of antibodies specific for neuraminidase type 1 (N1), 2 (N2) and 3 (N3) in avian sera. A total of 1450 sera from different avian species (854 negative, 185 positive to N1, 136 positive to N2, 219 positive to N3 and 56 positive to other N subtypes sera) were analysed in parallel by the three ELISAs. ROC analyses were performed to enable the selection of best cut-off values and estimation of diagnostic specificity and sensitivity. In addition, the correlation between the new developed ELISAs and the neuraminidase inhibition test was evaluated on a limited number of sera. The validation process of the three ELISAs proved excellent diagnostic performances, with very high specificity and sensitivity, ranging from 99.4 to 99.8% and from 97.6 to 100%, respectively in the three assays. The discriminating potential between antibodies elicited against homologous and heterologous N validates the test for use in "DIVA" assays, to distinguish between vaccinated and infected birds.