The carcass of a great horned owl (Bubo virginianus), which had been found moribund in southern Ontario, was presented for necropsy. Throughout the liver and spleen were numerous white foci 1-2 mm in diameter; also noted were white plaques in the mucosae of the pharyngeal papillae and intestine. Results of light and electron microscopic studies and experimental transmission to two captive great horned owls suggested that this was a herpvirus disease similar and possibly indentical to the owl disease reported by other workers in Wiconsin and Australia.