Marek's disease(MD) is a lymphoproliferactive disease of chicken caused by highly infectious cell-asscioated oncogenic alpha-herpesvirus MD virus serotype 1(MDV1), characterized by lymphoproliferactive infiltration in visceral organs, muscles, and peripheral nerves.Recently MD has been well studied mainly because of two reasons. One is the heavy economic losses worldwide from MD following industrial poultry farming system in the 1950s and 1960s.The other is the important position of MDV on tumorigencity and vaccine prevention from malignant neoplasm. Because MDV is the first herpesvirus proved to be oncogenic with experiment. In addition, MD is the first and only disease that can be successfully prevented by vaccination with antigenically related nonpathogenic or attenuated virus strains and good management practices. The research for tumorigencity of MDV infection is of great significance on comparison biology as MD model for oncogenic herpesviruses.To date, the development of MD lymphomas has been studied at two different but interlating levels, the host cells and the virus. Recently the study on the disease is mainly focused on MDV. A number of excellent reviews on this topic cover the historical, serotype, oncogenic, and immunologic aspects of MDV infection. But a little is about tumorigencity of lymphoma and the relationship between lymphoma development and telomere or telomerase activity.Teloemic ends of chromosome is special structure named telomere, which plays an important role on keeping integrity, replication, andlocalization of chromosome. Telomere-telomerase hypothesis was established on the research of the relationship between cancer and senescence on the basis of the phenomena that telomerase has no activity hi most of the normal somatic cells but it is activated in human tumor cells. It is clear that rising in telomerase activity accompanies with the growth of tumor cells. It is implied that telomerase activation is a marker for tumor formation. Integrated MDV is the maui pattern at the cell lines derived from MD lymphomas. The integration sites were characteristic for the individual cell lines and were referentially located at the telomeres of large-and mid-sized or mini-chromosomes. The telomere is a good site for integration. According to those references, we try to investigate the host cells, especially chicken genome structure of telomric ends of chromosomes.The host cell genome of MDV artificially infected was investigated in this study. The study was performed on the MDV DNA integration status and integration site in host cell and correlationship between MDV DNA integration and telomere / telomere-associated sequence with MD model. We try to find tumorigencity.Telomere associated sequences were cloned and sequenced in chicken tissues. The results showed that comparing with a -like sequence within TRL ,TRS, and junction of IRL&IRS of MDV genome, the homogeneity of TAS1&TAS2 of chicken is 76.2% and 93.7% respectively. The homologeneity between TAS of mice and chickens is lower than those mentioned above, which is 50.9% and 59.1% respectively. Besides, there is higher polymorphism in chicken's TAS. We deduce that there might be a correlation between MD tumor and telomeric ends of host cells.The patterns and sites of chicken chromosomes on which two TAS were located , first time, were determined via FISH assay. Integration sites of MDV were mainly located at the telomeres of large-and mid-sized ormini-chromosomes derived from MD chicken cells, which is similar with integration MDV in cell lines derived from MD lymphomas. We predict that chicken's telomeric end region is an excellent site for MDV integration. Meanwhile we also established techniques for chromosome specimen preparation.With MD model derived from artificial infection of MDV to chicken, we investigated status of MDV localization in MD host cell genome via special sequence of MDV genome by FISH assay. The results showed that integration sites are mainly located at telomeric ends of large-and mid- si