Soluble extracts of melanoma specimens were prepared by 3 M KCl extraction. Delayed cutaneous hypersensitivity reactions to these antigens were noted in 25 of 39 melanoma patients and 7 of 30 patients with other neoplasms. Only 4 of 34 melanoma patients reacted to an extract of autologous muscle. Maximum reactivity to these antigens occurred at 24 hr and was demonstrated histologically by skin biopsy. Chromatography on Sephadex G-150 resulted in two fractions that elicited delayed cutaneous hypersensitivity reactions in melanoma patients. These fractions were subjected to polyacrylamide gel electrophoresis. The first region of the Sephadex 1 gel reacted in 8 of 13 melanoma patients and only 1 of 7 patients with other neoplasms. Some activity was found in other regions of the gel. Skin test activity was confined to the second polyacrylamide gel electrophoresis region of the Sephadex II gel, to which 7 of 9 melanoma patients reacted compared with 1 of 7 patients with other tumors. Recovery of antigenic activity in excess of the total present in the original extract after partial purification indicated that inhibitors of delayed cutaneous hypersensitivity reactions present in the crude KCl extract were removed. A 20-fold increase in antigenic activity per unit protein was achieved.