Interferon-gamma has pleiotropic adjuvant effects on host defenses. These effects have made interferon-gamma particularly useful for enhancing host defenses in patients with chronic granulomatous disease of childhood and thus for reducing the incidence of life-threatening infections in these patients. Increasingly, data suggest that interferon-gamma will be useful for treating infections characterized by intracellular persistence in macrophages, such as toxoplasmosis, leishmaniasis, and mycobacteriosis. Interferon-gamma is emerging as an important cytokine for use in the treatment of infectious diseases.