CSF from 40 MS patients and 30 individuals with other neurologic diseases were analyzed using isoelectric focusing (IEF) in polyacrylamide gel method. The IgG bands were identified by immunofixation using specific goat anti-human IgG serum. CSF from 28 of 40 MS patients (95%) showed 10-15 distinct oligoclonal bands with different isoelectric points and varying intensities. In contrast, CSF from patients with other neurologic diseases showed a number of diffuse IgG bands in IEF after immunofixation. CSF from 30 of 40 MS patients (75%) showed 1-4 oligoclonal IgG bands in agarose gel electrophoresis (PANAGEL), however, the resolution of bands was generally poor. When 34 coded CSF specimens were analyzed in the IEF and immunofixation procedures, 15 of 17 MS patients (88%) showed distinct oligoclonal IgG bands. Thus, IEF in combination with immunofixation is a superior method for detecting oligoclonal bands in CSF and provides a more valuable tool for the diagnosis of MS. The results also showed that a number of distinct individual oligoclonal IgG bands of MS CSF were of either kappa-type or lambda-type, suggesting that these bands are monoclonal. IgG isolated from 12 of 17 MS sera (70%) showed oligoclonal bands in IEF partly similar to those seen in CSF in the pH region 8.5-9.3; whereas, those from other neurologic diseases showed diffuse bands.