Because of their impact on human and veterinary health, there is considerable interest in understanding how Culicoides use olfactory cues in host location. The adequate chemical stimulus for sensilla located on the maxillary palps was determined for several species of female Culicoides. Electrophysiological studies identified and characterized the sensory neurons on Culicoides maxillary palps that responded to stimulation with low concentrations of CO₂. The concentration response function in different background concentrations of CO₂ was established for C. furens (Poey), C. stellifer (Coquillet) and C. mississippiensis Hoffman. Comparisons were made to previously studied CO₂-sensitive neurons in mosquitoes. Understanding what sensory signals the host releases and how they are detected may lead to the development of strategies aimed at controlling these insects.