The roles of interleukin (IL)-6 and IL-8 in mediating the symptoms and signs of influenza A infection were examined. Adults were intranasally inoculated with a rimantadine-sensitive strain of influenza A HlNl virus and treated with rimantadine or placebo. Viral shedding, secretion weights, symptom scores, and concentrations of IL-6 and IL-8 in nasal lavage fluids were compared between treatment groups. Viral shedding was associated with increases in local and systemic symptoms, in expelled secretion weights, and in levels of IL-6 and IL-8. Compared with placebo, rimantadine treatment reduced viral shedding, systemic symptoms, and levels of IL-8. Days of viral shedding and IL-6 but not IL-8 concentrations were significantly correlated with the other measures of symptoms and signs. These data support a causal relationship between viral replication, cytokine production, and symptom expression, and they suggest that IL-6 may have a role in mediating symptom and sign expression during influenza A infection.