Parenchymal brain tumors, which were metastases of primary lung cancer, were surgically removed from 25 patients. During the operation, patients were administered (intravenous or intracarotid) 100 mg/sq m of cis-diamminedichloroplatinum (CDDP) and postoperatively, they received intravenous CDDP at 3-month intervals for 1 year. The results of this mode of treatment were compared with those obtained in 25 patients who underwent the same surgery but received other anticancer agents and in 39 patients who received no postoperative chemotherapy. Patients in the CDDP-treated group survived much longer than both of the other treatment groups. In the CDDP, but not in the other two groups, survival was significantly longer in patients who had undergone resection of their lung tumors than in those who had not. The stage of lung cancer was not found to significantly influence survival time among CDDP-treated patients. Brain metastasis was the cause of death in 12% of the patients who received CDDP, in 16% those treated with other drugs, and in 26% of those who received no chemotherapy. The incidence of local and remote intracranial tumor recurrence, including meningeal carcinomatosis, was similar in the three groups. However, the mean interval from resection of the metastatic brain tumor to local or remote recurrence was longer in the CDDP-treated group than in the other two groups, and the 2-year-survival rate was significantly higher after CDDP administration. These results suggest that CDDP may be useful in the therapy of metastatic brain tumors derived from lung cancer.