We present the results of susceptibility tests conducted on the sandfly Phlebotomus argentipes, the vector of visceral leishmaniasis in India. Adult P. argentipes insects were collected from 42 villages in 6 districts of the state of Bihar, India, as follows: Patna, Vaishali, Muzaffarpur, Samastipur, Sheohar, and Sitamarhi. These adult insects were exposed to 4% DDT-, 5% malathion-, and 0.05% deltamethrin-impregnated papers using a WHO test kit by following the standard procedures. In 16 (38.1%) of 42 villages surveyed, the P. argentipes populations developed resistance to DDT. Susceptibility tests using the organophosphate malathion in 22 villages revealed that in 1 (4.5%) village, the species developed resistance to this insecticide. P. argentipes was, however, highly susceptible to the synthetic pyrethroid deltamethrin. For long-term vector control of P. argentipes, it will be necessary to overcome the threat of insecticide resistance in this species.