The single most important respiratory pathogen in infancy and early childhood is respiratory syncytial virus (RSV). Approximately 40% of primary RSV infections in children result in lower respiratory tract disease. Approximately 1% of RSV-infected children require hospitalization. Especially in high-risk children, primary RSV infection results in significant morbidity and, sometimes, death. This high-risk group includes children with bronchopulmonary dysplasia, children with congenital heart disease, premature infants less than 6 months of age, and children with immunodeficiency diseases. It has been estimated that, in the United States, 14,000 infants with chronic lung disease and 16,400 infants with heart disease will be identified by 12 months of age. More than 91,000 children are hospitalized annually with lower respiratory tract disease caused by RSV, and 4500 deaths occur. In 1985 a report from the Institute of Medicine calculated that the annual hospitalization costs attributable to RSV infection were $300 million. Data collected at the New England Medical Center in 1991 show that the average cost of hospitalization of a child with RSV was $808 each day. Because of difficulty in developing a safe and effective RSV vaccine, attention is now focused on passive immunization using an RSV immune globulin. On the basis of a recently completed multiinstitutional trial, RSV immune globulin appears to be a safe and cost-effective option for prevention of severe RSV disease in high-risk children.