Two populations of feedlot cattle--weaned calves and yearlings--suffered otitis media. In calves the disease was acute and epizootic and had a prevalence of about 400 cases per 2000 cattle, whereas in yearlings, it was chronic and sporadic and had a prevalence of 1 case per 2000 cattle. Clinical signs were facial paralysis, otorrhea, and head tilt. The middle ears from 64 dead calves and 22 dead yearlings were examined. Calf ears had acute infection, with exudate in air cells and rupture of tympanic membranes. Yearling ears had chronic infection, with exudate in air cells, rupture or destruction of tympanic membranes, and necrosis of air cell partitions. Mixtures of Pasteurella multocida and Corynebacterium pseudotuberculosis were isolated from diseased ears, but Pasteurella multocida predominated in acute infections and Corynebacterium pseudotuberculosis predominated in chronic infections.