Haemorrhagic enteritis (HE) of turkeys is an economically important viral disease of turkeys, not only because it causes high mortality and immunosuppression, but also due to increased slaughterhouse condemnations. The disease is characterized by haemorrhagic enteritis and necrosis of lymphoid cells and a proliferation of reticuloendothelial cells in the spleen. In marble spleen disease (MSD), in addition to splenic changes, pulmonary congestion and oedema are also seen. Whereas splenomegaly in chickens (SMC) is characterized by lesions in the spleen similar to those of HE and the pulmonary lesions of MSD. The causative agents of HE of turkeys, MSD of pheasants and SMC are serologically indistinguishable group II Aviadenoviruses. All the three viruses can be propagated in lymphoblastoid cell lines derived from Marek's disease virus induced lymphoma in turkeys viz. MDTC-RP-16 and MDTC-RP19. The infection can be diagnosed by isolation and characterization of aetiological agents, serological tests such as the agar gel precipitation test, enzyme linked immunosorbent assay and the use of immunoperoxidase to demonstrate intranuclear adenovirus-like particles in infected cells shown by electron microscopy. The control of HE is possible by vaccination using avirulent MSD virus of pheasants as well as avirulent or attenuated strains of turkey HE virus.