A study was undertaken to find the effect of repeated bites of the sandfly, Phlebotomus argentipes, on its host as well as on the vector itself. The study also aimed to find the effect of the immune serum on the parasite, Leishmania donovani, naturally transmitted by the vector. The hamster which was exposed to sandfly feeding showed good antibody titre against the sandfly salivary-gland secretion, which indicates that the salivary-gland secretion is immunogenic in nature. The result also revealed that the feeding attraction of the females, which has been expressed as the percentage of engorgement, gradually decreased as the mortality rate increased during the subsequent bites. Similar mortality rate was observed when the flies were fed with the immune sera through an artificial membrane feeding method. When the sandflies were fed both with the immune sera and the blood-parasite (L. donovani) suspension, in addition to the major loss of the number of vectors, there was an inhibition of development in the gut and a concomitant reduction in the migration of the parasite in the surviving females. These results indicate that the anti-sandfly saliva immune sera probably bind with the respective antigen-presenting sites of the sandfly salivary gland and, thus, cause the sandfly death. The possible explanation of the inhibition of the forward movement of the parasites is that the attraction of the parasites to the oesophagus, mediated by the sandfly saliva, is inhibited by the anti-saliva antibodies. The importance of anti-sandfly saliva antibodies as a tool of vector control and also to block the transmission of leishmaniasis has been indicated.