The main purposes of making deflection measurements are to assist in the evaluation of the structural condition of roads, and to help in the design of road strengthening measures. In developing countries in the tropics the high road temperatures and other climatic effects necessitate the use of a special technique in making deflection tests. This report describes the techniques adopted by the TRRL for the measurement of pavement deflection in tropical developing countries, and discusses factors relevant to the deflection of road pavement in such conditions