A truncated version of the white spot syndrome virus (WSSV) 27.5 kDa envelope protein was expressed as a histidine tag fusion protein in Escherichia coli. The bacterial expression system allowed the production of up to 10 mg of purified recombinant protein per liter of bacterial culture. Antiserum from a rabbit immunized with the recombinant protein recognized the 27.5 kDa viral envelope protein of WSSV isolated from different geographic regions. The antiserum did not recognize any of the other known WSSV structural proteins. A sensitive immunodot assay for WSSV was developed using the specific rabbit polyclonal antiserum.