A 72 year old patient suddenly experienced severe lumbar pain irradiating into the right leg. Later on, weakness of the muscles thigh appeared. A thorough radiological investigation which showed degenerative alterations of the vertebral column did not supply an explanation. After a pathological titer against Borrelia burgdorferi was found in serum and radiculitis was detected on EMG, the diagnosis of Lyme-Borreliosis of the nervous system could be confirmed by analysis of the cerebrospinal fluid. Under intravenous antibiotic treatment with Ceftriaxone (2 to 4 g daily for three weeks) the symptoms regressed completely, and the pathological findings in the CSF regressed. The significance of some findings in CSF in relation to Borreliosis of the CNS.