There are definite immunologic abnormalities associated with the cancer bearing state which are apparent on both in vitro and in vivo testing. The weight of evidence presented suggests an increasing loss of immunocompetence with increasing disease stage and a degree of positive correlation of immunologic responsiveness with prognosis. Unfortunately the correlation is not absolute for any one individual, although it is often fairly well defined for a large group of patients. This is a failure of all other prognostic studies as well. The critical question as to whether or not this loss of immune integrity reported represents a cause or a result of cancer progression remains largely unanswered. The data suggests that the measured impairment of immunologic responsiveness stems from conditions brought about by the tumor bearing state. Regardless of which precedes the other, the cancer or the immunoincompetence, the additional question as to the effect of immune impairment on the disease progression also remains uncertain. Results of tests to monitor immunocompetence appear to be of some value if used as additional data on which to base prognostic conclusions. Dinitrochlorobenzene skin testing is an assay that is easily performed and probably yields the most easily obtained significant prognostic information.