This paper deals with observation of the morphology of DHV,applying immune electron microscopy,and histopathologic changes of embryonating chicken eggs inoculated with DHV.DHV particles were spherical,without envelope and 15-20 nm in diameter.Ten-day old embryonating chicken eggs inoculated with DHV were killed and examined histologically under the light microscope and electron microscope at regular intervals up to the death of the infected embryos.Histopathologic changes seen under the light microscope included lymphocyte infiltration of the liver sinusoids,degeneration and necrosis of the hepatic cells,congestion and hemorrhage of the liver,lymphocyte infiltration of the pia mater encephali and capillary blood congestion of the cerebrum.Electron microscope examination of the liver revealed many vesicles in the intracellular space of the hepatocytes,high electron dense particles in the cytoplasm,cytoplasmic vac-uoles and shrunken nuclei.Finally,the nuclear membranes wrinkled and ruptured.Theplasma membianes burst and crganelles spilled or disappeared.Brain cells observed under the electron microscope showed that the endoplasmic reticulumdilated and formed small vesicles.The nuclear membrane also ruptured and organelleswere released.Viruslike particles were found in Disse's space and in the membrane-limited vesiclneithe cytoplasm near the cell membrane.