This work consit in na experimental analysis about the influence of combined bending and torsion preloading in fatigue strength of steels, under variable plane bending. It has been shown that combined bending and torsion preloading has little influence in fatigue strength for lifes (10)3 less than N less than 10 cycles. In this range, the most significant influence is 13,97 per cent, corresponding to (10)3 cycles and an quivalent axial preloading 0 m 4 equal 45,8 kgf/ mm. However, for a life n more than 5x 10 cycles we have found no influence with preloading from zero zero to 63,7 kgf /mm. Using hypothesis testes, with 90 per cent confidence level, we have proved that there is no influence of preoloading when 17,4 less than mi less than 63,7 kgf / mm. This has been observed for any life N between (10)3 and 10 cycles. The maximum distortion energy theory was adopted as a flailure theory, applied to alternating and medium components separately. It was used a test specimen with fine ground surface finishing fatigue stress concentration factor 1,1 per cent (neglected) effective cross section in bending for preloading and for the alternating component. In the final statistical analysis it was the Weibull distribution fuction. The fatingue machine was specially designed in our laboratory to obtain the necessary data.