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Background & objectives: Impact of indoor residual spraying of DDT on malaria transmission andvector density was evaluated in six villages of Shergarh PHC, Bareilly district, Uttar Pradesh under theoperational condition of National Vector Borne Disease Control Programme (NVBDCP) from July 2001to March 2002 (one transmission season only).Methods: Two rounds of DDT (50% WDP) spraying @ 1 g/m2 were done both in the experimental andcontrol villages by the state health authorities. The spraying in experimental villages was supervisedby Malaria Research Centre (MRC) whereas the district health authorities supervised the operation incontrol villages. Mass blood surveys were made three times— before the first round, in between thefirst and second rounds and after the second round of spraying. The blood smears were examined bythe trained microscopists of MRC, Haldwani. From the above examinations epidemiological indicatorssuch as slide positivity rate (SPR), slide falciparum rate (SFR) and infant parasite rate (IPR) werecalculated. All malaria positive cases were given radical treatment as per NVBDCP schedule.Entomological parameters such as per man hour mosquito density, parity rate, gonotrophic conditionand adult susceptibility status of Anopheles culicifacies to diagnostic dosages of DDT (4%) weremonitored as per the standard techniques.Results: A total of 988.5 kg of DDT was consumed during two rounds of spray. The house coveragevaried from 87 to 95.3%. Parasitological evaluation revealed significant reduction in malaria cases (p <0.0005) and infant parasite rate declined from 2.9 to 0%. Entomological observations revealedconsiderable reduction in the density of malaria vector An. culicifacies despite of its 21.4% mortalityagainst DDT test papers.Interpretation & conclusion: The overall results of the study revealed that DDT is still a viableinsecticide in indoor residual spraying owing to its effectivity in well supervised spray operation andhigh excitorepellencyfactor.