The susceptibility of Phlebotomus papatasi to DDT was studied in field surveys at localities in different areas of Iran during 1985-88. In many parts of Iran houses had been treated with DDT for malaria control (1950-68). Tests were carried out in localities where the application of DDT had been discontinued since 1969. This investigation showed that P. papatasi from Isfahan is more tolerant to DDT than flies from other areas, probably a manifestation of DDT resistance.