An attempt was made to neutralize white spot syndrome virus of shrimp using the antiserum against recombinant VP28 protein of WSSV. The dilutions of virus stock ranged from 1 × 101 to 1 × 108 were used to determine the dilution resulting in 90-100% mortality in Penaeus monodon by intramuscular injection of WSSV. A constant amount of WSSV (at 1 × 0104) was incubated with various antiserum concentrations and injected into shrimp. No shrimp died in the negative control injected only with NTE buffer. The shrimp in the positive control, which were injected with WSSV only showed 100% mortality at 10-day post infection (d p.i.). The WSSV preincubated with preimmune serum caused 100% mortality of shrimp at 10 d p.i. None of the shrimp injected with the preimmune serum only died. When the WSSV was preincubated with two or one time diluted anti r-VP28, shrimp mortality was 100% and 75%, respectively, at 50 d p.i. apparently the anti r-VP28 at these dilutions is not able to neutralize the WSSV. When the WSSV was preincubated with undiluted anti r-VP28, none of the shrimp died, indicating that WSSV can be neutralized by the anti r-VP28 in a dose-dependent manner. © 2005 Elsevier B.V. All rights reserved.