Summary:As known from inflammatory diseases, oligoclonal bands in the cerebrospinal fluid (CSF-OCB) may indicate a humoral immune response within the central nervous system. Previous studies on the CSF IgG content in Alzheimer disease (AD) have been controversial about the relationship of OCB and elevated IgG indices. To explore this problem, we combined qualitative (isoelectric focusing) and quantitative methods (IgG index) to detect intrathecal IgG production and related these findings to the presence of blood-cerebrospinal-fluid barrier (BCB) dysfunction. Fifty-one AD patients were compared with patients with vascular dementia (VD), major depression (MD), multiple sclerosis (MS), and age-matched control subjects. CSF-OCB could be traced in 20% of AD patients. An elevated IgG index was found in 6% and a BCB dysfunction in 16% of all AD patients. Either intrathecal IgG synthesis or BCB dysfunction were detected in a subgroup of 36% of all AD cases and in 40% of patients with late-onset AD. Intrathecal IgG synthesis and BCB dysfunction may suggest underlying immunological or inflammatory changes in an as-yet undefined subgroup of AD patients and support the notion of a heterogeneous nature of AD.