Interleukin-2 (IL-2) mutants having reduced toxicity, which include full-length IL-2, truncated forms of IL-2 and forms of IL-2 that are linked to another molecule are disclosed herein. Particular substitutions within IL-2, particularly within the permeability enhancing peptide region of IL-2 achieve substantial reduction of vasopermeability activity as compared to a wildytpe form of the mutant IL-2 while retaining many of the immune activating properties of IL-2. Invention IL-2 mutants can be used to stimulate the immune system of an animal and may be used in the treatment of various disorders and conditions.