The data of 772 patients were analyzed for albumin, immunoglobulins, glucose, and cell counts in cerebrospinal fluid and serum in healthy controls and in patients with various neurological disorders. Using laser-nephelometric end-point determination the IgG/albumin index was established for controls; a value smaller than 0.85 was considered normal. This index was used to distinguish between impairment of the blood-brain barrier and thecal synthesis of immunoglobulins. No correlation was observed between glucose concentration and cell counts in cerebrospinal fluid. Together with the IgG/albumin index, determination of IgA and IgM increased the sensitivity to detect multiple sclerosis from 43 to 58%.