Respiratory syncytial virus (RSV) is the most important respiratory pathogen in infancy and early childhood and may predispose to subsequent lower respiratory tract illness. Recent data indicate that RSV up-regulates the substance P receptor, making the airways abnormally susceptible to the proinflammatory effects of this peptide released from sensory nerves. The present study was designed to determine whether the administration of RSV antibodies prevents the potentiation of neurogenic inflammation in rat airways. Five days after inoculation, sensory nerve-mediated extravasation of Evans blue-labeled albumin was significantly greater in the airways of RSV-infected rats than in pathogen-free controls. Polyclonal immune globulin enriched for RSV-neutralizing antibodies (RSVIG) reduced neurogenic extravasation when injected 24 h before intranasal inoculation of the virus but not when injected before endotracheal inoculation. A humanized MAb against RSV fusion protein (palivizumab) was twice as potent as RSVIG when given before intranasal inoculation and also caused significant inhibition after endotracheal inoculation. Furthermore, palivizumab inhibited neurogenic inflammation in RSV-infected rats when given 72 h after virus inoculation. These data suggest that palivizumab protects the respiratory tract from RSV-induced inflammation when given before or in the early phase of the viral infection. The administration of palivizumab to high-risk infants may limit the severity of the acute airway inflammation and may protect against subsequent lower respiratory tract illness.