In this work, changes in the cerebrospinal fluid in acute and chronic polyneuritis as well as in the Guillan-Barré-Strohl syndrome are discussed and and it is pointed out that a specific coordination of the inflammatory cerebrospinal fluid syndromes to certain pathogens or noxae cannot be made. For the differentiation of the Guillain-Barré-Strohl syndrome and existence of increased gamma-globulin bands with identical mobility in the serum is pointed out. In myelitic disease pictures, acute and chronic cerebrospinal fluid syndromes are distinguished also in the cerebrospinal fluid according to the clinical course; regular changes, however, cannot be derived. Syphilitic cerebrospinal-fluid syndromes can easily be differentiated by their immunoactive findings. In multiple sclerosis, we distinguish between typical and atypical changes in the cerebrospinal fluid. Above all, the oligoclonal bands, i. e. the discontinuous proceeding of the gamma-globulin zone and the existence of several bands in the agar gel electrophoresis, play an essential role. In 95 per cent of the cases, oligoclonal bands can be shown. There are no greater differences with respect to oligoclonal bands between intermittent and chronic-progressive courses. For the differential diagnosis of haemorrhagic syndromes, the cerebrospinal fluid cell picture can make a considerable contribution. Macrophages loaded with erythrocytes indicate that a haemorrhage occurred 12 to 18 hours before; macrophages loaded with haemosiderin indicate a haemorrhage that occurred 6 to 8 days before; and macrophages loaded with erythrocytes and haemosiderin indicate a seeping haemorrhage or an event that occurred several times. The Nonne-Froin syndrome indicates a massive protein increase often with a regular or only slightly increased number of cells. The importance of the Queckenstedt tests is pointed out. A particular role is played by meningitis carcinomatosa et sarcomatosa with the demonstration of a great number of tumour cells.