The purpose of this project was to isolate recombinant antibodies for diagnosis of very virulent infectious bursal disease virus (vvIBDV) in fixed tissues. Phage-displayed recombinant antibodies, comprised of the single chain variable fragment (scFv), were investigated. A previously made recombinant antibody library generated against vvIBDV was selected and screened for recombinant antibodies that reacted against vvIBDV in ELISA. A new library was constructed fom chickens immunized with fixed vvIBDV and also screened for recombinant antibodies against vvIBDV. Also, a previously identified recombinant antibody, known to react well with vvIBDV, was used to replace either the Vh or VI gene with corresponding fragments from a new library. The Vh and VI antibody genes were initially amplified effectively by PCR. No new recombinant antibody clones were isolated from the libraries generated against vvIBDV. However, exchanging the Vh or VI genes from a known recombinant antibody with genes from a new library showed that the heavy chain was essential when binding to vvBDV. Light chains could be exchanged without loss of activity, but when heavy chains were exchanged, all activity was lost. The light chains were found to create new binding properties when combined with the essential heavy chain. The recombinant antibody clones were sequenced, analyszd and characterize.