Anopheles stephensi, the main vector of malaria in the province of Fars, Southern Iran, is resistant to DDT and dieldrin. Resistance to DDT was first recognized in 1957 and then to dieldrin in 1960. Since 1968 this species has been under pressure of malathion house spraying, 50% w. d. p., 2g/m2, 1-2 rounds per year. In recent years, agricultural pesticides such as malathion and carbamates are commonly used on a number of crops. Tests carried out with malathion-impregnated papers during 1975 showed a change in the susceptibility level of A. stephensi. The object of the present paper is to summarize and discuss briefly the field investigations concerning insecticide resistance in A. stephensi.