White spot syndrome virus (WSSV) is the causative agent of the white spot disease of shrimp. Penaeus monodon were captured from Muttukadu Estuary in Chennai, India, transported to the laboratory and maintained in an aerated system with continuous water circulation-biofiltration. WSSV-free P. monodon were challenged by feeding them only once with WSSV-infected tissues of P. monodon. Cumulative mortality (100%) of the infected individuals was determined. Tissues from infected and uninfected shrimp such as muscles, hepatopancreas, heart, gills and eye tissues (100mg of each) and haemolymph (50 microl) were subjected to SDS-PAGE. In infected muscle tissue, six newly expressed proteins were detected. In infected haemolymph, four new proteins and three intensely expressed high molecular weight proteins were observed. Three intensely expressed high molecular weight proteins were detected in infected heart tissue and two new proteins in infected hepatopancreatic tissues. In infected gill tissues, two new protein bands and three intensely expressed high molecular weight proteins were detected on comparison with uninfected tissues. Similarly, two intensely expressed protein bands were seen in the infected as compared with the uninfected eye tissues. The protein profiles of the muscle tissue from 50 different naturally infected (WSSV) shrimp were analyzed. Eleven different new protein bands appeared in the infected muscle tissues when compared to the control muscle tissues whereas; in muscle tissue six new proteins were observed both in naturally and experimentally WSSV infected shrimp. The current study has shown that the protein expression patterns of the infected tissues of P. monodon have been drastically altered by WSSV infection. Western blot analysis revealed that one of the newly expressed 53 kDa protein in the infected muscle represents the WSSV envelope protein.