A mosquito surveillance program was established in 1983 on Indian reservations in Iowa, Nebraska and South Dakota. Standard New Jersey light traps were operated on 12 reservations throughout the summer seasons in 1984 and 1985. Rainfall levels in general were higher than normal at all sites in 1984 but were lower than normal at most sites in 1985. Aedes vexans was the most abundant species collected on all reservations and Culex tarsalis second in abundance. Man-biting collections of mosquitoes near Brookings in 1984 reached 35 mosquitoes/5 minutes in early July and were largely composed of Ae. vexans, Ae. dorsalis and Ae. nigromaculis while numbers of Cx. tarsalis and An. quadrimaculatus were minor. During the same period in 1985, man biting collections averaged less than 5/5 minutes.