Effects of intrathecal cytostatic chemotherapy on the clinical symptoms and cerebrospinal fluid (CSF) findings are being demonstrated in a case of metastatic carcinoma of the breast with signs of meningeal irritation and cranial nerve involvement. Clinical symptoms disappeared after repeated intrathecal applications of methotrexate. CSF cell counts were reverted to normal but tumor cells were found to be persistant in CSF over a period of 19 months. Risks of combined intrathecal and systemic cytostatic therapy and possible effects of parenteral citrovorum factor applications are being discussed. The importance of continued intrathecal chemotherapy and of regular and thorough examination of CSF cells in meningitis carcinomatosa is emphasized. Cytological methods included investigations on viable CSF cells.