Generation of infectious particles of infectious bursal disease virus (IBDV) has been essentially performed by transfecting susceptible cells with in vitro synthesized cRNAs of genomic segments A and B. In the present study, we have explored the possibility to proceed directly in vivo without taking into account the extra-genomic vector-derived sequences. For this purpose, cDNAs of segments A and B were subcloned into an eucaryotic expression vector under the control of the immediate early CMV promoter. Upon transfection of primary culture of chicken embryonic fibroblasts with both constructs, a cytopathic effect (CPE) typical of that produced by IBDV could be observed, indicating that the 5'- and 3'- vector-derived extra-nucleotides did not interfere with the replication and packaging process. Finally, in order to develop a GFP-based packaging assay, we first tried to express this fluorescent protein in the context of the IBDV polyprotein encoded by the genomic segment A. Our initial results indicate that the presence of IBDV specific sequences upstream of the GFP polypeptide dramatically decreased the fluorescence of the latter protein.