One hundred one patients were treated for Ph' positive chronic granulocytic leukemia (CGL) in the blastic phase. In seven of these (6.9 per cent), meningeal leukemia developed. Of the 99 patients who died of their disease, a complete remission was achieved in 12 with a median survival of 12 months (three to 28 months). Incomplete responders had a median survival of only 2.5 months (one to 14 months). In five of the 12 complete responders (42 per cent), but in only two of the incomplete responders (2.3 per cent), meningeal leukemia developed. The principal neurologic signs were cranial nerve palsies and papilledema. All patients had pleocytosis with myeloblasts in the cerebrospinal fluid. As in patients with acute leukemia and diffuse histiocytic lymphoma, increased survival of patients in whom hematologic remission from the blastic phase of CGL is achieved may allow sufficient time for the development of meningeal leukemia. Intrathecal methotrexate is extremely successful in treating this complication. Cerebrospinal fluid pleocytosis was eradicated in all seven of our patients, and neurologic symptoms and signs were completely eliminated in five patients. No evidence of meningeal leukemia was found in three of the five patients in whom an autopsy was performed.