In a group of 31 patients with a confirmed diagnosis of multiple sclerosis the authors assessed the presence of oligoclonal abnormality of gammaglobulins in cerebrospinal fluid. Specimens of non-concentrated cerebrospinal fluid were examined by two separating methods which use as a vehicle polycryamide gel: isoelectric focusing and a modified electrophoretic technique. By isoelectric focusing an oligoclonal state was proved in 71%, the finding was doubtful in 16.1% and negative in 12.9%. The applied electrophoretic separation revealed an oligoclonal state in 58.1%, the finding was doubtful in 25.8%, negative in 16.1%. In cerebrospinal fluid where isoelectric focusing did not prove an oligoclonal finding, the latter was not detected by electrophoresis either. The method of isoelectric focusing is obviously more sensitive than mere electrophoretic separation. In common practice, it is, however, better to use electrophoresis in vehicles which positively influence the separation process, best in a polyacrylamide gel. Only when the finding is negative or doubtful and there is urgentclinical suspicion, it is suitable to supplement the examination by isoelectric focusing.