Early diagnosis based on immunoenzymatic techniques requires significant amounts of immunoreagents. Hence, using directional cloning technology, a 38-KDa fusion protein containing a complete coat protein (CP) gene or Citrus tristeza virus (CTV) encoded by the expression vector plasmid (Pinpoint™ Xa3, Promega) with a fragment of biotin binding protein (BBP-rCTV-CP) was highly expressed and purified from E. coli cell culture. Antiserum obtained from rabbits after injection with the BBP-rCTV-CP fusion protein showed comparable reactivity in the serological detection of CTV. This antiserum could be used at dilution or 1: 10.000 at the detection stage in an indirect ELISA (IDAS-ELISA) and was efficient for trapping the virus in standard ELISA. These polyclonal antibodies reacted with a wide range of CTV isolates from different Egyptian geographic sources, and or different biological properties.