Determinations of albumin and immunoglobulin G (IgG) were performed in paired cerebrospinal fluid (CSF) and serum samples from 24 subjects with schizophrenia. These determinations allowed calculation of two indices, one that is an indicator of integrity of the blood-brain barrier and the other a measure of selective IgG production within the central nervous system (CNS). In comparison with previously determined reference values, 7 of 24 (29%) subjects showed increased blood-brain barrier permeability, and 8 of 24 (33%) demonstrated elevated endogenous CNS IgG production. One of these eight also demonstrated oligoclonal banding on high-resolution protein electrophoresis of the CSF.