MX-2, a new morpholino anthracycline derivative, showed broad anti-neoplastic activity against experimental tumors. Molecular weight of MX-2 is 622.07, and it can cross blood-brain barrier because of its high lipid solubility. In this report, we described its in vitro and in vivo effects on brain tumors. The growth of rat 9L and human KNS-42 glioma cells were markedly inhibited by the medium containing more than 1 ng/ml of MX-2. The inhibitory concentration of MX-2 for 50% cell kill was 1.8 ng/ml for 9L cell and 18 ng/ml for KNS-42, respectively. These values were the almost same as those reported with P388 leukemia. In rats with meningeal carcinomatosis induced by intracisternal inoculation of Walker 256 carcinosarcoma cells, the median survival time was significantly prolonged. The increased life span was 40, 40, 40 (p less than 0.01), and 20% (p less than 0.05) in the animals given intravenous MX-2 of 1.5, 1.0, 0.75, and 0.375 mg/kg on day 1, 5, and 9 after tumor inoculation respectively. These results indicate that MX-2 may be a promising new antineoplastic agent for the treatment of malignant brain tumor.