Despite enormous efforts to find a specific laboratory test for multiple sclerosis, agar gel electrophoresis of the CSF proteins has remained the next to the best one. This study presents evidence that thin layer polyacrylamide isoelectric focusing of the CSF gamma globulins is by far superior for this purpose. In effect, about 91% of the 262 multiple sclerosis patients studied had oligoclonal fractions present in the very alkaline region of the pH gradient. Of the same group of patients only 65% did show pathological results when studied by agar gel electrophoresis. Of the 272 CSF samples from patients suffering from other neurological diseases, only about 7% showed the presence of oligoclonal bands in the same region of the pH gradient, when submitted to isoelectric focusing.