Interferon-alpha (IFN-alpha) given orally has biological activity in humans and other animals. The dose providing the most benefit delivers IFN-alpha to the oral mucosa in a concentration (10(2)-10(3) IU), similar to that naturally produced in the nasal secretions during respiratory infections. In contrast, conventional IFN therapy employs parenteral doses of > 10(6) IU and, for this reason, orally administered IFN therapies have been called low-dose treatments. Efficacy in both animal disease models and human studies has been reported, and the mechanisms whereby oral administration has a systemic effect are under active study in a number of laboratories.