We report a method for displaying the affinity distribution of a polyclonal antibody population using sodium thiocyanate elution followed by an ELISA detection technique. We have used this method to study the affinity distribution of antibodies in samples of CSF and serum from patients with MS, and compared the results to those obtained from patients with viral encephalitis. Patients with MS had predominantly low affinity antibody against a particular antigen whilst patients with a primary viral infection had predominantly high affinity antibody against the causative organism.