The chicken monoclonal antibody (mAb), 6D-12-G10, reacts with an apical complex protein at the anterior tip of E. acervulina sporozoites that inhibits parasite invasion in vitro. Because this mAb was produced at low amount from the original hybridoma cells, an scFv antibody was constructed by amplification of the corresponding V-H and V-L genes and expressed in E. coli. The scFv antibody was produced at a minimum of 7 mg l(-1) and exhibited virtually identical antigen reactivity as the original mAb.