The insecticide susceptibility of Aedes aegypti adults and larvae from Santo Domingo, Dominican Republic, was investigated using World Health Organization standard procedures. A field strain was more resistant to insecticides than a colony strain that originated from the same place. Larvae produced from ovitrap-collected eggs were resistant to temephos (78.2% mortality on exposure to 0.025 mg/liter). Mortality rates after exposure of adults to discriminating concentrations showed that wild populations were resistant to DDT, malathion, propoxur, permethrin and deltamethrin. The problem of resistance was considered serious enough to warrant consideration of control measures other than the use of chemicals.