Fatigue limit data of 304L stainless steel and 1045 carbon steel are used to evaluate a recently developed critical plane model for multiaxial fatigue of metals containing small defects. The model is based on the square root of the area parameter and is designed to reflect the Mode I-dominated physical damage mechanism of small defects. The concept of directionally dependent fatigue strength is introduced to extend the critical plane definition to defects whose projected area varies with the plane. The Walker relation with a critical plane interpretation is proposed to account for the mean stress effect. The experiments were performed on specimens with small cylindrical holes under a variety of axial, torsional, and axial-torsional loading conditions, including the presence of mean or static stress. Different nonproportional loading paths were used to study the multiaxial fatigue behaviour. A detailed observation of the direction of the small cracks originated from the holes, at or just above the fatigue limit, was carried out. The model is found to give good estimates of both fatigue limits and crack directions.