ABSTRACT: The causative viral agent was purified from diseased shrimp Penaeus monodon with white spot syndrome. Negatively stained preparations show that the virus is pleiomorphic. It is fusiform or rod-shaped. In negatively stained preparations, the virion measures 70 to 150 nm at its broadest point and is 250 to 380 nm long. In some virions, a tail-like projection extends from one end. The capsid is apparently composed of rings of subunits in a stacked series. The rings are aligned perpendicular to the longitudinal axis of the capsid. The genome of the virus is a double-stranded DNA molecule which produces at least 22 Hind III fragments. The full length of the DNA is estimated to be longer than 150 kbp. Based on the morphological characteristics and genomic structures of the virus, we confirm that white spot syndrome associated virus (WSSV) is a member of genus NOB (Non-Occluded Baculovirus) of the subfamily Nudibaculovirinae of Baculoviridae, name the present isolate PmNOBIII, and propose the use of WSBV (Baculovirus associated with White Spot syndrome) to indicate PmNOBIII related agents.