Viral respiratory illnesses are among the most common afflictions in the United States. Until recently, few agents were available to control these infections. Now, there are specific and nonspecific agents either to prevent or treat viral respiratory infections. For example, a better understanding of the pathogenesis of the common cold provided new insights into therapeutic intervention for that entity. In other instances (eg, influenza), the antiviral agent is so specific that there is a need for diagnostic information to guide therapy. Epidemiological clues, clinical symptoms, and some newer laboratory methods all contribute to the clinician\'s understanding of the cause of an individual respiratory illness and guide the choice of therapy. In other circumstances, information is being gradually developed that points toward the availability of a broad-spectrum antiviral drug with activity against at least five of the important respiratory viruses; its major limitation is that a cumbersome and expensive means of delivery to the patient is required. For such a drug to gain widespread use, a more practical method of delivery is necessary.