The end results of therapy of 346 patients with lung tumors, treated with surgery alone, are compared, depending on the type of general anesthetic agent used. Anesthesia was induced with ether in 220 patients, halothane in 103, and neuroleptanalgesia in 23 cases. All the anesthetic agents were administered in a mixture with nitrous oxide. The basic characteristics of patients, who were divided on the basis of anesthetic agent, were identical. The results show that type of anesthesia during surgical treatment for lung tumor has an effect on the end results of therapy, and the best prognosis is ensured when halothane is used. Further analysis established that the end results of surgery with halothane anesthesia are improved, when partial resection rather than radical pneumonectomy is performed, at stage 2 of malignant disease and when metastases into regional lymph nodes are absent. Such improvement may be explained by stimulation of the hypothalamo-pituitary-adrenal system as well as a relatively lower degree of immunosuppression and development of conditions more adverse for implantation of circulating tumor cells than in the case of ether or neuroleptanalgetic anesthesia.