Experiments are described in which an Amsler twin-disc machine was used to study the effect on pitting performance of sulphur as an extreme pressure additive. It was found that at 30 °C sulphur as an additive was detrimental to the pitting performance but at 100 °C sulphur as an additive was beneficial. Tribochemical reactions at these temperatures were studied and the effects of the reactions were related to the pitting performance of the lubricants. Other experiments using a Wöhler fatigue tester are described: the results of these experiments support the findings of the disc machine tests.