It has been proposed that a family of small soluble binding proteins, variously named as chemosensory proteins, sensory appendage proteins, pherokines and OS-D-like proteins, are involved in insect chemoreception. These proteins are present in a wide range of insect species and have a characteristic four cysteine motif. We have cloned cDNAs and gene sequences encoding these proteins from a number of aphid species, the first report of such in the order Hemiptera and supporting the view that these genes predate the divergence of the Neoptera. In one aphid species, Megoura viciae, we have shown that the proteins are present primarily in adults with one protein being most abundant in antennae and legs. This supports the view that the proteins could be involved in chemoreception but our preliminary binding studies failed to detect binding to a range of compounds which are known to elicit an electrophysiological response by aphids.