In a population comprising 197 patients serum and CSF proteins were assayed using the radial immunodiffusion technique devised by Mancini. Multiple discriminant analysis was applied to investigate whether the measured CSF/serum protein relations and their ratios could be regarded as an indicator of specific neurologic diseases. One significant finding was that the slope angle alpha of the regression line between the serum/CSF relation and molecular weight may represent an important indicative parameter. A small angle is suggestive of enhanced permeability of the blood-brain barrier, a large angle of a correspondingly lowered permeability. Further, the analyses demonstrated that the combined use several predictors can markedly improve differential diagnosis. The study also demonstrates the potential of a statistical analytic technique that is still rarely applied in medicine.