The present invention relates to C34 peptide derivatives that are inhibitors of viral infection and/or exhibit antifusogenic properties. In particular, this invention relates to C34 derivatives having inhibiting activity against human immunodeficiency virus (HIV), respiratory syncytial virus (RSV), human parainfluenza virus (HPV), measles virus (MeV), and simian immunodeficiency virus (SIV) with long duration of action for the treatment of the respective viral infections.