High-dose interleukin-2 (IL-2) is the only approved immunologic therapy for advanced melanoma, but response rates are low and significant toxicities limit treatment to otherwise healthy patients. g209-2M is a nanopeptide engineered to mimic an epitope of the gp100 melanocyte differentiation protein that is recognized in a human leukocyte antigen (HLA)-restricted manner by melanoma tumor-infiltrating lymphocytes in some patients. Previous reports indicated that administration of the g209-2M peptide could induce g209-reactive circulating T cells in patients with melanoma and that the combination of g209-2M and high-dose IL-2 might be a more active treatment than high-dose IL-2 alone. Low-dose IL-2 is not active but has significant biologic effects, and because of a different toxicity profile, it can be offered to most patients. The primary objective of this cooperative group phase 2 study was to determine the activity of the combination of g209-2M and low-dose IL-2 in advanced melanoma. Twenty-six HLA appropriate patients with advanced melanoma received subcutaneous g209-2M peptide once every 3 weeks and subcutaneous IL-2 (5 million IU/m) daily for 5 days during the first and second weeks. Patients were monitored for tumor response, toxicity, and induction of g209-reactive circulating T cells. There were no objective responses. There were no toxic deaths and no grade 4 toxicities. More than half of the patients experienced some grade 2 toxicity and one quarter experienced grade 3 toxicity. There was no convincing evidence by enzyme-linked immunospot or tetramer analysis of induction of g209-reactive circulating T cells. The combination of g209-2M and low-dose IL-2 is safe and tolerable but inactive against advanced melanoma. Absence of evidence of immunization raises concerns for peptide-based immunization strategies with concurrent IL-2.