Five patients with chronic meningitis were hospitalized several times for progressive neurological symptoms. The clinical manifestations included cranial neuritis, radiculoneuritis, myelitis and encephalitis. In two cases cerebral infarction occurred. The course was commonly characterized by a tendency to deteriorate. From the clinical point of view, it was repeatedly difficult to exclude multiple sclerosis or tuberculous meningitis. Finally, specific antibodies against Borrelia burgdorferi were detected by indirect immunofluorescence assay. The diagnosis of a borreliosis was not considered initially because there was no history of tick-bite or erythema chronicum migrans, and the neurological involvement of the central nervous system seemed unusual. The latency between the first symptoms and diagnosis varied from 3 months to 5 years. After a parenteral, high-dose therapy with penicillin, there was a significant improvement in all patients. In two cases, there was evidence of intrathecally produced antibodies to myelin basic protein.