Tests to evaluate the susceptibility level in Anopheles gambiae s.1. and Culex quinquefasciatus from Ouagadougou and two nearby villages have been carried out. Anopheles gambiae s.1. larvae from Ouagadougou showed complete susceptibility to organophosphates and carbamates, and adults showed low level resistance to DDT. Nine percent survival of adult An. gambiae s.1. to one hour exposure of 4% DDT was observed in samples from Zaghtouli village while in those from Koubri village, where dieldrin also was tested, resistance to both organochlorine insecticides was detected. Culex quinquefasciatus showed susceptibility to fenthion, malathion, fenitrothion, and chlorpyrifos, whereas incipient resistance to temephos was detected. Electrophoretic analysis showed polymorphism of high and low active esterases (Est-2 + Est-3) confirming the association between OP resistance and enhanced esterase activity in this species.