Susceptibility levels of adult vector Anopheline mosquitoes in Iran were studied in field surveys during 1970-1974. Tests were carried out by WHO standard methods. The development of physiological resistance to DDT and dieldrin in A. stephensi is probably the most serious technical problem encountered in the malaria eradication campaigns in Southern Iran. Resistance to DDT was observed in 1957 and to dieldrin in 1960. In later tests throughout the country resistance to both insecticides was confirmed. In Southern Iran malathion was applied since 1968, but no resistance was observed up to this date. A. Fluviatilis and A. Superpictus are still susceptible to DDT, despite widespread residual spraying. Tests showed no resistance to dieldrin. After DDT applications for 10-14 years tolerance in A. Sacharovi showed that this species is resistant to DDT in Moghanshahr, Azarbaijan province in the Northwest and tolerant in the Izeh area of Khuzistan province in the Southwest. This species is susceptible to dieldrin and malathion. Resistance of A. Culicifacies to DDT and susceptibility to dieldrin and malathion were shown through tests in Baluchestan in May 1973.