The paper contains the tatigue tests results for specimens made of three cast irons under proportional and non-proportional variable amplitude tension with torsion. The experimental data for long fatigue life have been compared with those calculated according to the algorithm with use of the modified criterion of the maximum normal stress in the critical plane. In the considered algorithm the Palmgren-Miner hypothesis of damage cumulation seems to he useless whereas the Serensen-Kcgaycv hypothesis gives satisfactory results. Applying the method of fatigue damage cumulation we obtain the critical plane direction which agrees with the experimental fracture plane very well.