Infants and young children undergoing their primary infection with common human respiratory viruses are at risk of serious, even life-threatening, lower respiratory tract infection, A multiplicity of viruses infect the human respiratory tract but a relatively small number are responsible for the majority of significant illness. Of these the most commonly diagnosed in the pediatric population is respiratory syncytial virus (RSV), which infects essentially all children in their first or second year of life, bringing approx 1% into the hospital with bronchiolitis or pneumonia (1 ). Children with underlying cardiac or pulmonary disease, or born prematurely are particularly at risk. The virus also causes problems in the immunosuppressed and mortality rates are alarmingly high for RSV pneumonia after bone marrow transplantation (2 ). The availability of therapy with ribavirin (3 ) or high titer anti-RSV γ-globulin (4 ), which may be of benefit in these at risk groups, places a premium on rapid and accurate, but cost effective, diagnosis.