10.22376/ijpbs.2019.10.1.p1-12 Volume 8 Issue 2 2017 (April - June) To control a variety of vector borne diseases insecticides and insect repellents are used. They share a common mode of toxicity, and are used together inside and outside the living areas. The present study was designed to evaluate the insect repellents N,N-diethyl benzamide (Deb), N,N-diethyl phenylacetamide (Depa) and N,N,-diethyl metatoluamide (Deet) in combination with insecticide deltamethrin (Del) in rats. The study was conducted in 2 phases. Phase I was determination of LD lessThan sub greaterThan 50 lessThan /sub greaterThan of Del by Gad and Weil moving average method and LD lessThan sub greaterThan 50 lessThan /sub greaterThan of Deb, Depa and Deet by Dixon Up and Down method. Phase II was determination of LD lessThan sub greaterThan 50 lessThan /sub greaterThan of insect repellents in combination with insecticide by Dixon Up and Down method in rats. Among the four, Del was more toxic than the insect repellents. Among the repellents, Deet was least toxic chemical. The estimated LD lessThan sub greaterThan 50 lessThan /sub greaterThan of Del, Deb, Depa and Deet were 129.7, 1035.1, 333.3 and 1894.1 mg/kg respectively. The extrapolated LD lessThan sub greaterThan 50 lessThan /sub greaterThan estimate of Del in presence of one LD lessThan sub greaterThan 50 lessThan /sub greaterThan of Deb, Depa and Deet was 65.9, 40.3 and 20.2 mg/kg respectively. The LD lessThan sub greaterThan 50 lessThan /sub greaterThan were additive and no potentiation was observed between the insecticide and the insect repellents showing they can be used together. ANITHA MAGESH, R. VIJAYARAGHAVAN, S. SENTHIL KUMAR, ANITHA ROY AND R.V. GEETHA Deltamethrin, Deb, Depa, Deet, combined toxicity, LD50, rats. 426-431