S. shorttii, a common phlebotomine sandfly species of Assam, was tested for susceptibility to commonly used insecticides, D.D.T., malathion and Fenitrothion in Kamrup district, Assam. Tests carried out by WHO test kits showed 100 per cent mortalities against discriminating concentrations of malathion (5 per cent) and Fenitrothion (1 per cent). With D.D.T., in 1 hr. exposure mortalities recorded were 54.5 and 64.4 per cent, whereas in 24 hr. exposure mortalities were 75 per cent and 90 per cent. The area has been under continuous D.D.T. spraying since the beginning of NMEP in 1958, and high selection pressure appears to have precipitated D.D.T. resistance in this partly exophilic species.