Abstract: Disease model was built up for control of infectious bronchitis-nephritis (IBN). Seventy 1-day-old chicks were divided into three groups named A, B and C (experimental group, control group and infected group). IBN virus was inoculated artificially to experimental group, and one day post-inoculation chicks in infected group were put into experimental group. Clinical signs were observed 4 times each day under conventional management, sick and died chicks were autopsied periodically for pathological changes observed and recorded. A few organs were sampled and fixed in 10% formalin, sectioned with paraffin and stained with Haematoxylin & Eosin. Histopathological changes were observed under microscopy, recorded according to servere extention as 1 to 4 plus symbol and drawed with curved line. The results indicated that nephrotic lesions appeared the serverest and lasting longer period, from the beginning at day 2 and last to day 20. The lung, secondly, represented pathological changes during day 5 to 16. The time of changes in liver was similar to it in lung, only a little bit mild in severity. The heart showed lesions at day 6 to 13. One day later, the similar pathologic changes were appeared. This indicated that the disease was very strongly infectious.

Key words: chicken; infectious broncheitis-nephritis (IBN); histopathologic changes; lesion’s curve