IN A GROUP OF 1,190 CASES of malignant melanoma reported in 1952, there were 29 instances in which the primary site of the tumor could not be discovered.1 Therefore, it could be said that 2.4 per cent of melanomas had cryptic location of origins, in which circumstances the diagnoses were made by microscopical study of metastatic lesions, usually in superficial lymph nodes. With an enlarging experience now of more than 2,000 cases, the same incidence exists of undetected primary melanomas. In the majority of these patients, the neoplastic disease makes its appearance first in regional lymph nodes, giving the clinical impression of lymphoma, because of the apparent absence of obvious cancer in adjacent skin. Of these 29 patients, only 2 (6.8 per cent) have achieved the status of definitive cures, both for more than a decade (11 and 21 years, respectively). Survival could hardly be expected for patients whose