This paper reports studies on the morphology, animal infection, serological diagnosis and epidemiological survey of REV. Electron microscopy showed that REV was a typical type C oncornavirus with a "benzene ring-like" structure. Animal infection demonstrated that there existed synergism between REV and Herpesvirus of Turkey (HVT), and their combined action was dangerous to chicks. Using fluorescent antibody and enzyme-linked antibody techniques on frozen sections, two methods were established for determining REV distribution in the body of infected chicks. Serological survey of 10 chicken farms in Guangdong Province revealed positive reactors in 8 out of 10 farms, and suggested that the possible reason for HVT vaccine failure at one chicken farm was that the HVT vaccine used had been contaminated with REV.