A monoclonal antibody, HPC-1, labels only amacrine and displaced amacrine cells in adult rat retina. Reactivity with displaced amacrine cells was demonstrated by double-label immunofluorescence with HPC-1 and ganglion cell-specific reagents. HPC-1 antibody reacts with a polypeptide of apparent molecular weight 35,000. HPC-1 antibody labels migrating amacrine cells in late embryonic retinas. The results define cell-specific gene expression in relation to migration of one subclass of CNS neurons.