Abstract To study surface failures of nitride-hardened gears, rolling fatigue tests were performed using nitride-hardened steel rollers as gear-tooth surface models. Surface failure of nitride-hardened rollers was by subsurface-initiated spalling under all contact conditions, nitriding depths and Hertzian stresses used. Cracks leading to spalling initiated at the case/core boundaries. White etching areas (WEA) were observed along spalling cracks. Electron probe microanalysis revealed that the WEA material was carbide. It is considered that there is a relation between the initiation of spalling cracks and the formation of WEA.