This invention provides nucleic acid molecules encoding mutant human interleukin 13 molecules showing varying specificity for the restricted (IL4 independent) IL13 receptor. The mutant hIL13 molecules include those made by substituting the amino acid residues that occur in the alpha-helix regions of native hIL13 with various other amino acid residues. Some of the mutants retain the ability to bind and cause signaling through IL13 receptors, while other mutants do not.