Agarose gel isoelectric focusing (IEF) and electrophoresis (EF) were compared for detection of CSF oligoclonal bands in multiple sclerosis (MS) and other neurological diseases. The CSF IgG/albumin ratio, the IgG-Index and the IgG synthesis per day in the CNS were also considered. IEF was highly sensitive, revealing oligoclonal bands in 100% of CSF from 40 clinically definite MS, while EF had a sensitivity of 70%. In 90 patients with other neurological diseases, IEF revealed oligoclonal bands in 25.5%, EF in 11.1%. The IgG-index was the most sensitive of the quantitative parameters.