We examined the intrathecal production of immunoglobulins (Ig) G, A, and M in 16 patients with Behçet's disease, 13 of whom have CNS involvement, and in 40 neurologic controls. Oligoclonal IgA and IgM bands were mainly detected in CSF samples from patients with active neuro-Behçet's disease and were documented to disappear when neurologic manifestations remit. Oligoclonal IgG bands, however, were not related to disease activity and were also found in some neurologic controls. High immunoglobulin index values were detected in both active and quiescent diseases and were high in some patients with impaired blood-CSF barriers. The study presented here demonstrates that CSF oligoclonal IgA and IgM may be helpful in monitoring CNS disease activity in neuro-Behçet's and could be useful in understanding the pathogenesis of this disease.