Three monoclonal antibodies were used to examine with immunocytochemistry the distribution of the glycine receptors and the related 93kd polypeptide in the adult goldfish brain (Carassius auratus). One immunoglobulin recognizes the 48kd strychnine-binding subunit of the receptor and the two others bind to the peripheral 93kd polypeptide which is coupled to the receptor molecules. Immunofluorescent spots were visualised with all three antibodies on the somatic and dendritic membrane of the cells. A differential intensity of immunofluorescence was detected in the three different brain regions examined: the brainstem, the cerebellum and the telencephalon. For both proteins, the highest fluorescence was observed in the brainstem, particularly on reticular and vestibular neurons. In the cerebellum both the density and the intensity of labelling was low. At the level of the Mauthner cell, an identified bulbar command neuron, the distribution of glycinergic receptors was identical with that of the 93kd polypeptide. Both subunits were visualized on the somatic and dendritic membrane up to their extremities. These proteins appear to be co-localized in neurons other than the Mauthner cell, since they are always co-expressed in the same brain region. Their distributions are comparable with that observed in the mouse and rat nervous system as reported from autoradiographic localization of [3H]strychnine binding.