During the past hundred years much data on the fatigue behaviour of a wide range of materials has been accumulated and it is now well known, as a result of service failures and laboratory tests, that stress concentrators whether mechanically formed or inherent in the material, can cause serious reductions in endurance.The work described in this note forms part of a project being conducted at the Aeronautical Research Laboratories, Melbourne, Australia on the effect of stress concentrations on the fatigue properties of materials. The primary aim of the project is to establish a series of fatigue curves for different materials under a wide range of theoretical stress concentration factors and to attempt to find a basis on which to assess the notch sensitivity of different materials. The first investigation was carried out on 24S-T aluminium alloy and tests on two additional aluminium alloys, annealed copper and an alloy steel are in progress.