Tumours were found to be responsible for deaths at rates of 11%, 5%, 1.2%, and 3% in native breed chicks, layers, broilers, and broiler breeders respectively. Sera and egg-albumen were monitored for presence of P-27 common antigen of avian leukosis virus (ALV) by ELISA test. Titer of endogenous virus was detected in most of poultry farms at various degrees. The highest percentages were detected in meat type chicken flocks (25%) and native breed chicks (33%) and the titer of endogenous virus was higher than the titer of exogenous virus. Marek's disease antibodies were detected in yolk and sera of dams as well as in serum samples of the offspring and the ratio was found to be correlated. Maternal antibodies of Marek's disease virus were detected till 3-4 weeks of age.