Avian Leukosis Virus Subgroup-J (ALV-J). Mycoplasma gallisepticum (MG) and MycopJasma synviae (MS) are important pathogens in chickens that cause severe economical losses in poultry industry throughout the world. Seven broiler grandparent flocks of Iran (six broiler strains) were sampled randomly at the ages of 8-63 wk (100 samples from each flock) for antibody detection to ALV-J, MG, and MS by ELISA. One sample C0.9%) of flock F was antibody positive to MG. About me MS. There were 2 (2.1%), 2 (2.1%), 2 (2.1%), 8 (8.7%), 4 (4.3%), 9 (9.8%) and 2 (2.1%) positive samples from those collected from flocks A. B. C D. E, F and G. respectively. However, in all flocks tested, the mean S/P ratio was < 0.5 and rlius all flocks as recommended by the manufacturer were antibody negative to MG and MS. All plasma samples collected from flocks A. B and D were negative for ALV-J antibody. However, there were 2 (2.9%). 39 (51%). 5 (6.6%) positive samples from those collected from flocks C, E, and F., respectively. Only me flock E was antibody positive to ALV-J (according To the manufacturers instructions), because in other flocks the mean S/P ratios were < 0.6. The findings of tills study showed that one of the broiler grandparent flocks in Iran exposed to the ALV-J virus.