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Article provides experimental results in the field of ultra-high cycle fatigue behaviour of C55 high grade carbon steel obtained at high-frequency loading (f ≈ 20 kHz, T = 20 ± 10 °C, R = -1). The results confirm a continuous decrease of fatigue lifetime beyond the conventional fatigue limit. Fatigue fracture surfaces were characterized by surface fatigue crack initiation in both high and ultra-high cycle region, what means that that influence of microstructure defects was not significant enough to cause the sub-surface crack initiation.