The gamma globulins in cerebrospinal fluid from almost all patients with multiple sclerosis migrate in agarose electrophoresis as abnormal discrete populations, so-called oligoclonal bands. Such bands have also appeared in cerebrospinal fluid from patients with other types of inflammatory pathology such as neurosyphilis, acute idiopathic polyneuropathy, and subacute sclerosing panencephalitis. The demonstration of cerebrospinal fluid oligoclonal bands may aid in the evaluation of patients with early or atypical multiple sclerosis. This report describes a simple method for demonstrating cerebrospinal fluid oligoclonal bands using readily available commercial reagents and apparatus. Oligoclonal bands were seen in cerebrospinal fluid from all patients with clinically definite multiple sclerosis, even though some had normal cerebrospinal fluid gamma globulin levels, and in most patients with presumptive multiple sclerosis or other inflammatory conditions of the nervous system. They were not seen in cerebrospinal fluid of control patients with a variety of other neurologic diseases.