1. Using the energy approach here proposed, we have derived an equation for the summation of fatigue damage. As rupture criterion we take part of the total energy dissipated by unit volume of the materials. 2. The linear hypothesis and the hypothesis of Cortain and Dollan represent limiting forms of the resultant equation for materials undergoing no strengthening processes and materials with substantial strengthening respectively. 3. The use of the proposed relationship for real construction materials is preferable to both the linear and the Cortain-Dollan hypothesis.