Brain metastasis is of frequent occurrence in patients with cancer of the lung. To ascertain if brain metastasis is preventable, 34 lung cancer patients without brain metastasis were treated with 4 cycles of VM-26 plus CCNU at 4-week intervals. As a control for comparison, an equal number of lung cancer patients free of brain metastasis were treated with chemotherapy protocol which did not include VM-26 and CCNU. The patients were monitored by clinical symptoms, signs and CT or MRI scan and were followed up for 4-12 months. The results indicate that none of the VM-26 plus CCNU-treated patients developed brain metastasis while brain metastasis occurred in 7 (20.5%) of 34 control patients. The difference was statistically significant (P < 0.05).