Sixty-two patients with lung cancer underwent the multitest before and after radiotherapy so as to assess the initial immune state and modifications induced by radiation therapy. In cancer patients, a significantly smaller number of positive skin reactions were encountered than in the controls. No statistically significant differences emerged between patients grouped on the basis of histotype, clinical stage and performance or otherwise of surgery. In living patients, higher values were observed than in patients who died. After radiotherapy, multitest values underwent a very slight decrease.