The generation and use of small particle aqueous aerosols (1.23 microns aerodynamic mass median diameter, GSD = 2.0 microns) containing ribavirin is described. Administered via aerosol, ribavirin will be deposited rather uniformly on the surface of the nasopharynx, the tracheobronchial tree and in the pulmonary area. Examples of aerosol-delivered dosages found to be effective in the treatment of respiratory syncytial virus infection and influenza A and B virus infections are as follows: 12.8 mg of ribavirin/hour for a 6-month-old infant weighing 7.5 kg, and 56.2 kg of ribavirin/hour for a 25-year-old adult weighing 62.5 kg. Drugs which are relatively insoluble in aqueous solutions can also be administered in small particle aerosol by using liposomes as a vehicle. The preparation of enviroxime, a potent anti-rhinovirus drug, in liposomes for aerosol use is reported here. Its antiviral activity in liposomes was found to be undiminished, but its cellular toxicity was greatly reduced. It was well-tolerated by normal volunteers and studies are planned to determine its clinical efficacy.