Neurostatin, a modified ganglioside in mammalian brain, is highly immunogenic. Fusion of spleen cells of Balb/C mice immunized with bovine neurostatin with SP2O myeloma cells, led to hybridoma producers of anti-neurostatin antibodies. Two, monoclonal, IgG secreters were selected that recognized the inhibitor in blots and tissue of cow, rat and pig. The lack of species specificity indicated that the molecular structure of the inhibitory epitope is similar in these mammals. That epitope was also present in other gangliosides of the b series, defining a new regulatory system of glial-cell proliferation and apoptosis. The antibodies further revealed the neuronal origin of neurostatin.