The article describes the requirements set for concrete-reinforcing steel bars as to their fatigue strength and presents types of fatigue tests as well as examples of test results. The work also describes the effect of selected factors on the fatigue strength of concrete-reinforcing steel bars, demonstrates problems accompanying experimental fatigue tests involving reinforcing bars and presents a fatigue tests methodology enabling the obtainment of valid test results, developed by Instytut Spawalnictwa. The methodology was validated while testing B500SP grade reinforcing bars of diameters restricted within a 8-25 mm range.