The present study describes pathological, immunohistochemical, and electron microscopic findings in the respiratory tract and skin of chickens naturally infected with avian pox virus. Respiratory distress, depression, and cyanosis were found in the chickens upon clinical examination. At necropsy, erosion, crusts, and nodules were observed on the comb, wattle, and eyelids. Histopathological examination revealed that the epithelial cells in the stratum spinosum were hyperplastic, and that their cytoplasm contained large, eosinophilic inclusion bodies. Epithelial hyperplasia was also prominent in the mucosa of the trachea and bronchi, with characteristic cytoplasmic inclusion bodies and severe submucosal accumulation of mononuclear cells. Avipoxvirus infection was confirmed by an immune positive reaction with antibodies against avipoxvirus within the cytoplasm of the hyperplastic epithelial cells and within the inclusion bodies, and by the electron microscopy of typical dumbbell-shaped poxviral particles within the epithelial cell inclusions.