Respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV3) are the major causes of lung disease in infants and children worldwide. Current therapy is limited to RSV, and is only marginally effective. Preliminary studies in laboratory rodents have shown that a therapeutic approach which combines a potent antiviral drug with a potent antiinflammatory drug effectively reverses the course of pulmonary disease while accelerating clearance of the viruses. The long-term objective of this proposal is to determine the optimum combination of antiviral and antiinflammatory drugs, develop an aerosol-delivery system for treating hospitalized infants and children, and then proceed to clinical trials. The cotton rat model of RSV and PIV3 disease will be used to evaluate the two criteria by which efficacy of therapy will be measured: acceleration of virus clearance, and reversal of pulmonary pathology.