Two newly developed research tools for wind turbine blade fatigue evaluation, called WISPER and WISPERX, are presented. WISPER and WISPERX are standardized variable-amplitude test loading histories that are based on operational flap loading measurements on 9 different horizontal axis wind turbines. These turbines cover a wide range of materials, rotor diameters and geographical European locations . This paper summarizes the general philosophy on fatigue loading reference sequences which has led to various standards that nowadays exist for a variety of structural applications. Major development steps of WISPER are reviewed, while the information contained herein will enable fatigue specialists to judge whether the standards WISPER and WISPERX may suit their test objectives. This paper has been prepared for presentation at the 12th ASME Wind Energy Symposium, held on January 31 - February 4, 1993 in Houston, USA.