Flying mosquitoes were collected at a pair of collection sites at different heights from the ground by a suction trap enhanced with 1 kg of dry ice in summer in 2001 and 2002, on the campus of Nagasaki University, School of Medicine, and on a small desert island in Nagasaki, Japan. One collection site was near a tree canopy (6-12 m above the ground) and the other one at about 1 m above the ground. At each collection site, the trap was operated for 24 h to collect both noctunal and diurnal species. The following 9 species were encountered ; albopictus (Skuse), Ochlerotaus nipponicus LaCasse et Yamaguti, Culex pipiens pallens Coquillett, Armigeres subalbatus (Coquillett), Cx. tritaeniorhynchus Giles, Cx. halifaxi Theobald,CX. bitaeniorhynchus Giles, Orthopodomyia anopheloides (Giles), Tripteroides bamubusa (Yamada). The proportion of mosquitoes collected near the tree canopy was calculated for 4 dominant species ; 3.9 (females) and 1.2% (males) for Ae.albopictus, 64.5% for females of Cx. pipens pallens, 19% for females of Ar. subalbatus and 26.7% for females of CX. tritaeniorhynchus. The vertical distribution of flying moscmitoes in relation to the location of their vertebrate host is discussed.