A study was carried out to determine the percentage of apoptotic hemocytes in WSSV-infected Penaeus monodon and Penaeus indicus at different time intervals by DNA fragmentation assay using flow cytometry and agarose gel electrophoresis. Shrimp were injected with WSSV, and hemolymph at different time intervals was collected to determine apoptotic hemocytes. Apoptotic hemocytes were increased in course of infection and were found to be higher in P. indicus in comparison with P. monodon. Furthermore, DNA fragmentation of WSSV-injected hemocytes was also evaluated by the agarose gel electrophoresis and characteristic intranucleosomal DNA ladder patterns were detected in the DNA extracted from hemocytes of WSSV-infected shrimp, but not in the DNA of hemocytes from uninfected shrimp. © 2006 Elsevier B.V. All rights reserved.