Junction activity is one of the well-recognized histologic features of primary malignant melanomas of skin and mucous membrane. Its absence in a pigmented tumor revealing cellular and nuclear pleomorphism, mitoses, and invasion is usually indicative of the metastatic nature of the neoplasm or represents a local recurrence. However, junction activity cannot be considered as the sine qua non of some primary cutaneous melanomas, as evidenced from the reports of Allen and Spitz1 and Allen2 concerning malignant blue nevi. These latter, as in the more familiar benign blue nevus, are devoid of junction activity except in the very rare instance in which they are compounded with a nevus of the junction type. Atavistic features of the blue nevus, such as fasciculation of tumor cells, intermingled chromatophores, and sclerosis of varying degree, are usually observed in the malignant variant. In addition, necrosis, intracytoplasmic vacuolation, and