Analyses of the cerebrospinal fluid (CSF) to determine the blood-CSF barrier function and to detect intrathecal IgG production are used in the diagnosis of neurological and psychiatric diseases. Therefore, accurate reference values for these parameters are of utmost importance. However, current reference values are based on 'reference groups' consisting of patients with psychiatric and/or neurological symptoms but without positive clinical findings and on groups of young students. The present study presents reference values for CSF proteins in a large sample (n = 105) of healthy individuals, with a large age-span (18-88 years of age). The parameter for the determination of the blood CSF barrier function, the CSF/serum (CSF/S) albumin ratio, was found to show an increasing variability in individuals over 45 years of age, suggesting a less stable blood-CSF barrier function than in younger individuals. The upper reference limit for the CSF/S albumin ratio was 6.8 for individuals under 45 years of age and 10.2 for individuals over 45 years of age. The IgG index, a dimensionless quotient for the determination of intrathecal IgG production, showed only a minor correlation with age and had an upper reference limit of 0.63.