Monoclonal antibodies (MAbs) were generated to six recombinant proteins (odorant-binding proteins; OBPs) of Manduca sexta. The specificity of each MAb was demonstrated by labeling six immunoblots, each of which contained samples of all six recombinant OBPs. The expression patterns of the six OBPs could be grouped into three classes: (1) one (GOBP1) was expressed in sensilla located throughout each annulus; (2) two (ABPX and ABP2) were expressed in the long sensilla trichoidea bordering a zone that was arranged as an arch on the periphery of each annulus; (3) three (PBP2, PBP3, and GOBP2) were expressed in shorter sensilla occupying a wedge-shaped mid-annular zone of each annulus. In female antennae, sensilla expressing these OBPs were intermixed, and the distinct zonation observed in the male antenna was absent. In males, PBP2 was co-expressed in exactly the same cells of the mid-annular zone as those expressing PBP3 and most of the same cells expressing GOBP2, although its expression overlapped with no or only a few sensilla expressing OBPs of class 1 (GOBP1) or class 2 (ABPX, ABP2). This overlap of expression or lack of overlap between PBP2 and the other OBPs for male antennae was mirrored in female antennae. In view of the restricted spatial expression of OBPs within an annulus and the diversity of possible dimeric combinations of OBPs that arises from the co-expression of multiple OBPs in a given sensillum, OBPs could contribute to the specificity of the olfactory responses of insects.