A low prevalence of oligoclonal IgG bands (OB) has been reported as a unique feature of Japanese multiple sclerosis (MS) as compared with Western MS. We compared the frequency of OB between isoelectric focusing (IEF) and agarose gel electrophoresis (AGE) in 59 Japanese patients with clinically definite MS [39 with conventional form of MS (CMS) and 20 with optic-spinal form of MS (OSMS)]. The frequency of IEF-OB in total MS was 54%, whereas that of AGE-OB was only 17%. When OSMS was excluded, the frequency increased to 77% by IEF, whereas it remained 23% by AGE. Our study strongly suggests that IEF is highly effective for detecting OB in Japanese MS patients.