DDT susceptibility of Anopheles darlingi was compared from the southeastern and northwestern regions of Colombia. Mosquitoes from southeastern Colombia (Puerto Lleras) were fully susceptible to DDT but in the northwest (Quibdo) LT50s were 14.3 times higher. This resistance appeared to be restricted to the Quibdo area. This is the first time that the DDT resistance has been detected in this important malaria vector.