Cerebrospinal fluid (CSF) and serum from 15 patients with narcolepsy were examined regarding presence of oligoclonal bands on isoelectric focusing, IgG index elevation as indicator of intrathecal IgG production and CSF/serum albumin ratios. Two of 15 patients (13%) showed oligoclonal IgG bands in CSF, one of whom had increased IgG index. Slight disturbance of blood-brain-barrier function as reflected by elevated CSF/serum albumin ratios was present in 4 other patients. The frequency of oligoclonal IgG bands in CSF from patients with narcolepsy is within the range of what is found in other neurological, non-inflammatory diseases. These findings do not support the hypothesis of an immune-mediated pathogenesis of narcolepsy.