Protein parameters in CSF and serum have been studied in ninety-three reference subjects. CSF/S albumin ratio is proposed to be superior to CSF-protein or CSF-albumin as a test of the blood-brain barrier function, while IgG-index = (CSF/S IgG ratio)/(CSF/S albumin ratio) is superior to CSF IgG/protein ratio or CSF/albumin ratio for the demonstration of IgG elevation in CSF due to synthesis within CNS. The two quotients recommended correct for variations of albumin and IgG concentrations in serum. When the serum proteins are within reference range, the CSF protein concentrations are mainly regulated by the permeability of the blood-brain barrier, while the influence of S-albumin and S-IgG is only secondarily. The CSF/S albumin ratio is age dependent, while IgG-index is not. A proposed graphical presentation of CSF/S albumin and IgG-index may facilitate the interpretation of these parameters in routine clinical work.