The chemoaffinity theory postulates the existence of cell-specific molecular signals that uniquely identify individual developing neurons. Such molecules are thought to promote both accurate axon outgrowth and the formation of correct synaptic connections. To identify candidates for such neuron-specific recognition molecules, we generated monoclonal antibodies that recognize surface-associated antigens expressed by individual identified neurons in the grasshopper embryo. Here we report on a molecular label that is expressed exclusively by two pairs of sibling interneurons in the developing CNS. Our experiments indicate that during axogenesis, this molecule is expressed at the surface of the growth cones of these cells, while during subsequent synaptogenesis, it becomes concentrated at the cells' developing terminal arbors. In both cases the molecule appears to be secreted by the labeled structures. This molecule, which we call TERM-1, is a glycoprotein with a molecular weight of approximately 48 kDa. The highly restricted spatiotemporal expression pattern of TERM-1 implies that individual developing neurons can acquire and retain unique molecular labels that may be important for neuron-specific outgrowth and target recognition.