The gene encoding the VP28 envelope protein of White spot syndrome virus (WSSV) was cloned into expression vector pET-30a and transformed into the Escherichia coli strain BL21. After induction, the recombinant VP28 (rVP28) protein was purified and then used to immunize Balb/c mice for monoclonal antibody (MAb) production. It was observed by immuno-electron microscopy the MAbs specific to rVP28 could recognize native VP28 target epitopes of WSSV and dot-blot analysis was used to detect natural WSSV infection. Competitive PCR showed that the viral level was approximately 10(4) copies/mg tissue in the dilution of gill homogenate of WSSV-infected crayfish at the detection limit of dot-blot assay. Our results suggest that dot-blot analysis with anti-rVP28 MAb could rapidly and sensitively detect WSSV at the early stages of WSSV infection.