A prospective randomized study to evaluate the effect of adjuvant intrapleural OK-432 immunotherapy after resection of lung tumor was conducted in 93 patients with primary lung cancer. Among them, 46 patients had had intrapleural OK-432 injection, 47 had not. In the meantime, serial measurements of serum immunosuppressive acidic protein, of serum interleukin-2 receptor and of the subpopulation of the peripheral blood cells and lymphocytes were performed in all these patients. Patient characteristics in these two groups (sex, age, histological type, pathological stage, type of operation, and performance status) were compatible. The results showed that adjuvant intrapleural OK-432 injection after resection had no beneficial effect on a patient's survival time. Patients who received intrapleural OK-432, had an increase in blood leukocytes, granulocytes and monocytes and serum immunosuppressive acidic protein level. But the cell numbers of total T cells, suppressor/cytoxic cells, helper/inducer cells and natural killer cells of peripheral blood were decreased in the OK-432 positive group. Over half of the patients had transient 1- or 2-day febrile reactions after intrapleural OK-432 injection. It was concluded that neither clinical observation nor immunological monitoring of peripheral blood could demonstrate a beneficial effect from intrapleural OK-432 immunotherapy after complete resection of the tumor.