While olfactory neurons of silk moths are well known for their exquisite sensitivity to sex pheromone odorants, molecular mechanisms underlying this sensitivity are poorly understood. In searching for proteins that might support olfactory mechanisms, we characterized the protein profile of olfactory neuron receptor membranes of the wild silk moth Antheraea polyphemus. We have purified and cloned a prominent 67-kDa protein which we have named Snmp-1 (sensory neuron membrane protein-1). Northern blot analysis suggests that Snmp-1 is uniquely expressed in antennal tissue; in situ hybridization and immunocytochemical analyses show that Snmp-1 is expressed in olfactory neurons and that the protein is localized to the cilia, dendrites, and somata but not the axons. Snmp-1 mRNA expression increases significantly 1-2 days before the end of adult development, coincident with the functional maturation of the olfactory system. Sequence analysis suggests Snmp-1 is homologous with the CD36 protein family, a phylogenetically diverse family of receptor-like membrane proteins. CD36 family proteins are characterized as having two transmembrane domains and interacting with proteinaceous ligands; Snmp-1 is the first member of this family identified in nervous tissue. These findings argue that Snmp-1 has an important role in olfaction; possible roles of Snmp-1 in odorant detection are discussed.