Parainfluenza virus types 1 to 4 (PIV1 to PIV4) are important human pathogens that cause upper and lower respiratory tract infections, particularly in infants and children. The claimed invention is directed toward novel methods for the inhibition of parainfluenza virus transmission to a cell involving the administration of synthetic peptide fusion inhibitors. These inhibitors are derived from the parainfluenza virus and vary in length between 16 to 39 amino acids. The peptides were identified by screening for the presence of fusion inhibitory motifs (e.g., ALLMOTI5, 107x178x4, and PLZIP) within the parainfluenza virus genome. A number of peptides were identified and their fusion inhibitory activities ascertained. These peptides should provide useful antiviral agents.