Lowenthal and colleagues, at the Neurochemical Research Laboratory of the Neurological Department, Antwerp, pioneered the application of agar electrophoresis to cerebrospinal fluid proteins. In this paper, they report, for the first time, multiple sharp gamma-globulin bands (g1, g2 and g3) in the cerebrospinal fluid of patients with multiple sclerosis, which are not present in normal individuals. Previous work by others, such as Elvin Kabat and Harold Landow in 1942, had suggested that gamma globulin could form within the central nervous system and then enter the cerebrospinal fluid. This study, however, provided the first unambiguous demonstration of an immune response within the central nervous system. In clinical practice, the advent of magnetic resonance imaging has reduced the frequency with which it is necessary to test the cerebrospinal fluid in the diagnosis of multiple sclerosis. But in the tricky diagnostic case, the finding of cerebrospinal fluid oligoclonal bands can be an indispensable ally, because it remains the only direct clinical test of the pivotal disease process: active inflammation within the central nervous system.