Patients with metastatic renal cell cancer and metastatic melanoma treated with high-dose interleukin-2-based immunotherapy were prospectively evaluated for the development of vitiligo. All patients seen in the Surgery Branch, NCI Immunotherapy Clinic, who had been followed for at least 1 year were evaluated. Of 104 patients with metastatic renal cancer none developed vitiligo, though vitiligo was seen in 11 of 74 (15%) patients with metastatic melanoma (p2 = 0.0001). No vitiligo was seen in 27 patients who did not respond to immunotherapy, although vitiligo was seen in 11 of 43 (26%) melanoma patients who had an objective response to IL-2-based immunotherapy (p2 = 0.0002). These findings provide further evidence that the presence of a growing melanoma can sensitize patients to melanocyte-differentiation antigens and that the immune response against these antigens is associated with cancer regression in patients undergoing immunotherapy.