Scanning electron microscopy was used to observe contact-chemoreceptor sensilla in the genae of the anterior vestigial mouthparts of female Gasterophilus nasalis. These were of the uniporous trichoid type and were surrounded by mechanosensory aporous trichoid sensilla of variable size. Contact-chemoreceptor sensilla could be involved in detecting different chemical substances, including the equine kairomo-nes that stimulate females to lay eggs on the hair of the host and/or the short-range sexual pheromones used in precopulatory courtship. Theprobable functions of these sensilla are discussed with reference to the current literature on the sensorial organs of muscomorphid dipterans.