For helicopter gears many aspects of design and manufacturing must be analyzed@ such as material cleanliness@ case depth and hardness@ tooth root shape and roughness@ and compressive residual stresses. Moreover@ these gears are designed to withstand loads in the gigacycle field@ but are also subjected to short duration overloads. Therefore a precise knowledge of the shape of the S-N curve is of great importance for assessing their in-service life. A single tooth bending (STB) test procedure has been developed to optimally map gear design parameters and a test program on case carburized@ aerospace standard gears has been conceived and performed in order to appreciate the influence of various technological parameters on fatigue resistance@ and to draw the curve shape up to the gigacycles region. The program has been completed by failure analysis on specimens and by static tests. Some accessory investigations@ like roughness and micro-hardness measurements@ have also been performed. Gigacycle tests confirm the estimations done on the basis of the shorter tests@ both in term of fatigue limit and of curve shapes.