A125I analog of chloroquine was given to three patients with malignant melanoma. Daily assay of radioactivity in blood, cumulative urinary and fecal excretion of redioactivity, and scintillation photoscanning of the patients were done for two weeks. Tissues were removed surgically at intervals of one to two weeks for radioactivity assay and pathologic study. These studies suggest that, with the scintillation scanner, this radioactive analog of quinoline can be used to delineate the extent of the primary melanoma, demonstrate whether palpable lymph nodes contain metastases from the melanoma, and demonstrate metastases to cervical lymph nodes that cannot be seen or palpated. These uses will provide information to the surgeon preoperatively which may aid him in planning his surgical approach.