Delayed hypersensitivity to DNCB and the inflammatory response to croton oil were evaluated in 144 and 121 patients respectively, prior to and 3 to 6 months following curative radiotherapy. Eighty-one patients had in vitro lymphocyte transformation by PHA; 59 (41%) were nonreactors to DNCB and 27 (22%) to croton oil; 29 of 59 (49%) initially anergic to DNCB became reactive following radiotherapy. Only 13 of 85 (15%) initially reactive became anergic. Similar improvement of the inflammatory response was obtained. Patients who became DNCB-reactive following radiotherapy had the same favorable prognosis as those who were initially reactive. Radiotherapy did not adversely affect either delayed hypersensitivity or the inflammatory response. There was a 50'6 decrease in PHA stimulation and lymphocyte count after treatment. No correlation was found between DNCB reactivity and lymphocyte transformation prior to or following radiotherapy. The evaluation of the effect of radiotherapy on cell-mediated immunity depends on the tests used. Cancer 3 5 : 16 16-1 620, 19 75.
HE COMPETENCY OF THE IMMUNE SYSTEM IS
T critical in achieving cure of cancer.
Any treatment which has a deleterious effect on this system may adversely affect survival.
There is controversy regarding the action of radiotherapy on the immune system. Local irradiation is known to decrease the number of circulating lymphocytes. l3 Some investigator~~**~ found that after radiotherapy there was a depression of cell-mediated immunity as measured by in vitro lymphocyte transformation. other^,^.'^ however, reported no decrease in delayed hypersensitivity to several skin antigens, including 2-4 dinitrochlorobenzene (DNCB). The following prospective study was undertaken to determine if radiotherapy has a deleterious effect on cell-mediated immunity as