Electrical coupling among 4 different types of horizontal cells in Cyprinus carpio was examined from the diffusion of the intracellularly injected Lucifer yellow. The type of horizontal cells was identified by a spectral response and by a distinct morphology when the retina was viewed in flat mounts under a fluorescence microscope. Lucifer yellow diffused from the injected cell into surrounding cells, and in all of these preparations, diffusion was limited to horizontal cells of the same morphological type. Axons of horizontal cells were found to be coupled, and also at axons the coupling is likely to be limited to the same cell type.