This work concerns the application of Design Of Experiments (DOE) statistical techniques to obtain empirical correlation between DeltaK_th and microstructural parameters.The choice of developing a statistical model not based on physical principles is due to the difficulties encountered in the past applying these kind of models.After the development of an apparatus to automatically obtain the DeltaK_th, AISI 304 stainless steel was tested searching for correlation between fatigue threshold, grain size and load ratio.The author designed a 2^2 factorial experiment applying the Design Of Experiments to obtain a statistical bilinear model.