A study into effects of surface defects on the rolling contact fatigue of brass and rail steel has been undertaken on a twin-disc rolling-sliding test machine with both oil and water lubrication. Furrows and dents were artificially introduced into the disc surfaces, and surface microcracks and pits were monitored by means of surface replication. The results showed that artificial dents only reduce the fatigue life of the contact with oil, but not water lubrication. With oil lubrication the fatigue failure initiates at the surface defect. However, with water as a lubricant the whole of the surface undergoes cracking with the defect having no preferential effect. The possible mechanisms behind this behaviour are discussed in this paper.