The objective of this study was to investigate, whether the presence of oligoclonal immunoglobulin M bands (IgM-OCB) in cerebrospinal fluid (CSF) from patients with a clinically isolated syndrome (CIS), which is suggestive for the first clinical manifestation of multiple sclerosis (MS), anticipates the risk of a relapse during a retrospective study period of 21-106 months (mean 60 +/- 25). A relapse would lead to the diagnosis of clinically definite MS. Paired CSF and serum samples from 42 patients with a CIS and positive intrathecal IgG-synthesis were tested retrospectively for IgM-OCB, which are exclusively present in CSF, but not in the corresponding serum. Isoelectric focusing and affinity blot were used and clinical follow-up was based on telephone interviews. IgM-OCB were found in the CSF from 31 of 42 patients (74%). There was no correlation between the presence of IgM-OCB, the number of such bands or the IgM-Index on the one hand and the risk of a relapse during the follow-up in the cohort studied, on the other hand. These data do not support the idea that the presence of IgM-OCB in CSF might predict an unfavourable course in MS.