Abstract: Respiratory syncytial virus, or RSV, is a cause of respiratory tract infection in humans and other animals. Replication of the virus relies in part upon the association of the nucleocapsid (N) protein with a phosphoprotein (P protein). The present invention describes the identification and sequencing of peptide fragments which bind to the P protein and which disrupt the interaction of the N and P proteins. Such peptides may be used to inhibit replication of RSV, and for treatment of patients infected with RSV. Further aspects of the invention relate to the use of such peptides in the diagnosis of RSV infection.