Human (RSV) and bovine (BRSV) respiratory syncytial virus cause similar infections of the lower respiratory tract. Therefore, experimentally infected calves are suited to the study of RSV-induced chronic bronchiolitis. Colostrum-fed calves aged 17-24 days were successfully infected with BRSV. BRSV strain 375 was applied as an aerosol on 4 consecutive days. Clinical symptoms were already evident on the 1st day after infection. The calves were necropsied 12 weeks after the first infection. Focal severe chronic bronchiolitis with atelectasis and focal bronchiolitis obliterans were demonstrated. The bronchiolar lumina were filled with secretion. Transmission electron microscopy revealed an alteration of the ciliogenesis and partial loss of cilia. Immunhistochemically virus P protein could still be detected, mainly in the epithelial cells of the inflamed bronchioli.