Abstract: In the beginning of 2009, chicken in the age of 15-week appeared the symptoms of suspicious Marek’s disease (MD) in some parental breeding farms of Henan province. Those sick chicken became marasmus and depressed. Their cockscombs were turning into pallor and crinkle. The anatomic pathology changes were: obvieusly enlargment of liver, spleen, lung, kidney and hearts with different size of gray tubercles; glandular stomach swelled like pellet; gasttic wall incrassate;there were hemorrhages, ulcer focus and different sizes of gray tuberculoses on the gastric mucosa. The changes of histology and pathology included: in heart, liver, spleen, lung, kidney, glandular stomach, bursa of Fabricant, thymus and so on, there were a great deal of polymorphic tumors cells appearing dispersion infiltration or focally gathered, in addition healthy structural organizations had been destructed. The result of agar-gel precipitin test (AGP) was positive for MD. According to the results of clinic symptom, pathology dissect, histology pathology changes and AGP,diagnosed that the disease was visceral MD.

Key words: Marek’s disease; diagnosis; chicken