Currently, the only diagnostic test routinely available for the sero-diagnosis of BFDV is the haemagglutination-inhibition (HI) assay. This test, whilst useful and applicable to samples from a wide range of psittacine birds, is not an ideal assay; it requires erythrocytes from live animals, virus purified from the feathers of infected birds and polyclonal antibody preparations in order to perform the assay. Variations in these reagents make consistency between tests difficult to achieve, underscoring the need for a new test with standardised reagents for the sero-diagnosis of BFDV infection which has led to the development of an antibody response. Presented here are the methods used to develop a novel 'blocking' (or 'competitive') ELISA (bELISA) for the detection of anti-BFDV antibodies in psittacine sera. The assay was developed using a baculovirus-expressed recombinant BFDV capsid protein and a newly developed monoclonal antibody raised against this protein. The assay was then validated with 160 samples from eastern long-billed corellas (Cacatua tenuiostris) vaccinated with the recombinant capsid protein and challenged with live virus and 82 samples from cockatiels known to be HI negative. The bELISA described here is a sensitive and specific diagnostic test and should have wide application for the sero-diagnosis of BFDV.