Sera of 106 multiple sclerosis patients and 103 closely matched controls were examined for Borrelia burgdorferi antibodies. The prevalence rate in multiple sclerosis patients was 14.2%, in controls 25.2%. Overall prevalence was 20.1%. Mean IgG antibody level was insignificantly higher in controls than in multiple sclerosis patients. Patients with a chronic progressive course of multiple sclerosis had an insignificantly higher mean borrelia antibody level, when compared with those suffering from relapsing/remitting form of disease.