In 137 patients with different kinds of cancer and different cancer stage, cell-mediated immunity was investigated by DNCB (dinitrochlorobenzene) and tuberculin test. These two skin tests were performed before and after cytostatic drug combination therapy. For a collective of cancer patients we found a positive correlation between skin reactions and prognosis and a negative correlation between skin reactions and cancer stage. After cytostatic drug therapy skin reactions could be significantly stronger. This could be observed in 50% when one test was positive before chemotherapy and in only 20% when both tests were negative before chemotherapy. There existed a significant correlation between an increased reaction after cytostatic drug therapy and objective tumor regression. When skin reactions decreased, tumor progression was seen in all cases. Due to these observations we use skin reactions as a good parameter for therapy results. When delayed cutaneous hypersensitivity impairs 2--3 weeks after chemotherapy, we then change the cytostatic drug combination immediately. We cannot say at this moment, whether an improvement of cytostatic drug therapy can be reached in this way.