Cerebrospinal fluid data on 25 patients suffering from various phenotypes of X-linked adrenoleukodystrophy have been evaluated neurochemically including cerebrospinal fluid/serum quotient diagrams. Intrathecal IgA production in 13 of 14 patients with cerebral adrenoleukodystrophy was the most sensitive parameter in cerebrospinal fluid and was not seen in any of the neurologically asymptomatic patients or in the patients with adrenomyeloneuropathy. A blood-cerebrospinal fluid barrier dysfunction was found in 9 of these 14 patients. Additional intrathecal IgG or IgM synthesis was observed in 3 patients each. In 1 patient with lumbar punctures before and after onset of neurologic symptoms intrathecal IgA synthesis was seen only after the appearance of neurologic symptoms. Repetition of lumbar punctures in 5 neurologically symptomatic patients with cerebral adrenoleukodystrophy revealed a similar pattern of intrathecal IgA synthesis with a tendency of decreasing IgA concentration. The pathophysiologic aspects of intrathecal IgA synthesis are discussed in relation to other demyelinating and inflammatory neurologic diseases.