Investigations on the influence of the specimen size on the fatigue resistance of high-strength concrete. The use of high-strength concrete for structures which are exposed to cyclic loading can be inefficient by the present normative regulations due to a considerable reduction of the compressive strength. For further investigations of the fatigue resistance for those concretes, the knowledge about the influence of the specimen geometry is required. The question is how the results of fatigue tests in the laboratory can be transferred to the fatigue resistance of concrete in structures. In this article, the first findings on the influence of the specimen size on the fatigue behavior of two high-strength concretes are presented. Therefore, cylinder sizes of d/h = 60/180 mm and 100/300 mm were tested. It has been shown that the smaller test specimens lead to significantly higher numbers of cycles to failure, especially for related stress ranges of S_o ≤ 0.7. The normalization of the applied fatigue stresses to the compressive strength of the respective specimen size does not seem to compensate the influence of the size. However, it can be assumed that the specimen temperature during the fatigue test could have a decisive influence on the stress conditions in the specimen and thus on the fatigue resistance.