One hundred untreated neuroborreliosis patients were investigated by IgG/IgM immunoblot to find out if different stages and syndromes are characterized by different patterns of their Borrelia burgdorferi specific immune responses in CSF and serum. Stage III (n = 10) was characterized by a broad, highly specific intrathecal immune response (the mean number of IgM bands in CSF was 3.1 and of IgG bands 6.3). All patients recognized one or more of the following proteins (p35, p21, p18) or the 5 kd glycolipid. In contrast, the immune response in stage II (n = 90) was less restricted (28%) and heterogeneous (mean number of IgM bands 1.4 and of IgG bands 3.4). It was mainly directed against the highly crossreactive p41 antigen (91%). The different clinical features of stage II were comparable regarding the intrathecal immune response. However anti-glycolipid and anti-p35, -p21, -p18 IgG antibodies were detected in a small subset of patients, mainly corresponding to more severe courses of the disease. Our data are compatible with a direct agent-related pathomechanism in neuroborreliosis. Antibodies against certain proteins and the glycolipid of B. burgdorferi seem to have a prognostic value as to the development of more severe disease or transition to stage III.