An outbreak of respiratory disease which spread to all cattle aged less than 7 years in two farms, in the village of Avusy (canton of Geneva), is briefly described. The course of the disease was more severe in older animals, which showed frequently symptoms of bronchopneumonia, than in younger ones. The disease lasted from 3 to 10 days. No deaths were reported.A virus antigenically related to the human respiratory syncytial viruses was isolated from the conjunctivo-nasal specimens of one animal in each farm. Evidence of the bovine origin of both strains was brought by the sero-conversions displayed by the cattle under study in neutralization and complement fixation tests and by some biological traits of the virus as well.