An investigation of a disease with clinical nervous signs, conjunctivitis and greenish diarrhea together with congestion of parenchyma tous organs and brain meninges in the acute cases and focal areas of liver necrosis in advanced stages in autopsied pigeons of 2 lofts of pigeons was carried out. The mortality rate was 20% and 30% in loft A and B respectively. All attempts for demonstration of the bacterial agents including chlamydia psittaci or fungi were unsuccessful. Herpesvirus was isolated from a number of birds examined from both lofts. The isolated virus produced pocks on the CAM of chicken embryos. Histopathology of the pock lesions of the CAM revealed areas of ectodermal hyperplasia. The embryonic liver contained several minute necrotic lesions. Single basophilic intranuclear inclusion bodies were observed in the ectodermal cells of the CAM and the hepatocytes surrounding the necrotic lesions of the liver. Ultrastructurally, viral particles typical for pigeon herpesvirus were demonstrated in these inclusions. The virus was sensitive to ether and chloroform and completely destroyed at 56°C for 30 minutes, 4% phenol. 4% formalin and 2 NaoH but not by pH4. The experimental infection of 8-week-old pigeons by inoculation of infected CAM suspension subcutaneously proved the pathogenic nature of the virus.