A newly developed mouse monoclonal antibody, GGR-41, was used to localize a novel species of gangliosides, GT1a alpha and GQ1b alpha, in the rat central nervous system. Intense immunoreactivity was found in the neuropil of the spinal cord dorsal horn, spinal trigeminal nucleus, solitary tract nucleus, superior colliculus, interpeduncular nucleus, hypothalamus and septal area. The results suggest that GT1a alpha and GQ1b alpha are expressed in the nerve terminals of a certain population of cholinergic fibers.