The selection of biting sites on a human host of three closely related mosquito species belonging to the African Anopheles gambiae complex (Diptera: Culicidae), Anopheles gambiae Giles s.s., An. arabiensis Patton and An. quadriannulatus Theobald, was investigated under controlled laboratory conditions. Although these species differ in host preference, they all showed a significant preference to bite the legs and feet, suggesting that a mutual not specifically human factor was involved in the selection of biting sites. In subsequent experiments with An. gambiae s.s. this factor was revealed by altering the position of the test person. In experiments with the test person sitting on a stool, the legs and feet were significantly preferred as biting sites, whereas lying on the ground, with the legs and feet sticking up, the latter body parts were bitten significantly less than the body parts closest to the ground (head, trunk and arms). The results indicate that mainly convection currents along the host are used by members of the An. gambiae complex in selecting a biting site. In contrast to An. gambiae s.s. and An. arabiensis, large numbers of bites by An. quadriannulatus also occurred on the head, possibly in response to exhaled breath. It is concluded that the selection of biting sites of members of the Anopheles gambiae complex is guided by convection currents and partially mediated by host odours.