Using sintered steels in ever more demanding applications require thorough understanding of the material behavior to be able to make reliable, optimal designs. One of the most common failure mechanisms of components in service is fatigue. Thus, reliable models for predicting fatigue strength is important, and one of the factors that need to be accounted for is stress concentrations. In this paper plane bending fatigue of a diffusion bonded alloy, Distaloy AQ, is investigated. Heat treated specimens with different notch sizes are tested, and the results evaluated using models based on critical distance, stress gradients, highly stressed volume and fracture mechanics. It was found that all models worked well but the models based on stress gradients and critical distance gave the lowest scatter compared to experimental data, whereas critical distance gave the highest scatter. The fracture mechanics model gave intermediate scatter, but used one less fitting parameter.