ABSTRACT: Subadult Penaeus monodon shrimp were sampled from 4 farms in Queensland, Australia. Histological observations on lymphoid organs showed the formation of abnormal cell foci, which resembled tubules lacking a central hemolymph vessel. These formations contained hypertrophied nuclei with marginated chromatin, vacuolated cells and inclusion bodies which stained positive with Feulgen\'s reaction. Male and female P. monodon broodstock were sampled from 1 farm and showed the same abnormal histological features within the lymphoid organ as the subadults. Electron microscopy revealed tightly enveloped, cylindrical particles, 163-200 nm x 36-63 nm, packed into paracrystalline arrays within the cytoplasm and infrequently within the nucleus. Arrays of virions were also observed within the cytoplasm of broodstock gill cells. Cross-sections of the particles revealed electron dense nucleic acid cores and envelopes. Nucleocapsids, 83-590 nm x 13-15 nm, were seen free and in vesicles within the cytoplasm. A negatively stained preparation of partially purified lymphoid organ revealed a nucleocapsid with one conical end. Lymphoid organ virus (LOV) resembles yellow-head virus (YHV) from Thailand in its morphology and cytopathology and rhabdovirus of penaeid shrimp (RPS) from the Americas in its cytopathology.