The scientific constraints on the measurement of suprathermal electron fluxes in the 1–500 eV energy range in the auroral zone are discussed. These constraints are used to define the characteristics of an electrostatic analyser to measure such fluxes. The design and calibration of such an instrument are described. The application of the instrument to measure details of atmospheric absorption of low energy electrons by utilizing its high energy resolution, and the application to measure detailed variations of spectrum and pitch angle distribution by utilizing its high sensitivity are discussed with reference to a number of rocket flights made from the northern auroral zone.