An aerosol formulation of aldesleukin, a recombinant form of interleukin-2 (IL-2), with potential immunostimulating activity. Upon IL-2 inhalation, this cytokine activates lymphokine-activated killer cells and natural killer cells, and induces expression of cytotoxic cytokines, such as interferon-gamma and transforming growth factor-beta. This may eventually halt tumor cell growth. Localized administration of IL-2 may decrease toxicity and increase efficacy.