The notion that the body may attempt the immunologic rejection of neoplasms by reacting against antigens unique to the tumor has received increasing attention in recent years. It has been suggested that such activity occurs continuously, and that the growth of a tumor may signify a failure of this protective or "surveillance" mechanism.1 The nature of the immunologic response is thought to be the same as that responsible for the rejection of homografts. This involves a complex interaction among lymphocytes, macrophages and antigens, with the resultant infiltration of the offending tissue by activated lymphoid and phagocytic cells. These are thought . . .