We have developed an ultrasensitive isoelectrofocusing (IEF) method for the detection of oligoclonal (OGC) IgG bands in cerebrospinal fluid (CSF) and sera. In this procedure, double antibody and peroxidase immunodetection have been substituted by a single antibody labelled with alkaline phosphatase. Alkaline phosphatase immunodetection not only improves tenfold the sensitivity of the assay but also gives a sharper pattern resolution making the interpretation easier and increases the specificity of this technique. This preliminary report should be validated in a larger number of patients with and without multiple sclerosis (MS).