The paper describes the results of an experimental project on the running-in of circumferentially-ground steel discs operating under conditions of elastohydrodynamic lubrication. The experiments were performed on a two-disc machine in which the discs are loaded together in nominal line-contact. A special feature of the machine is the facility for obtaining surface profiles from the discs without the need for disturbing them during the course of an experiment in which they are run-in by incremental loading. Using this facility it was possible to measure the disc surfaces at frequent intervals during a running-in test.Relocation profilometry was used to follow the development of individual surface profiles during running-in. The effect of running-in on various surface parameters was investigated using two different lubricants. The first lubricant was a medium viscosity mineral base-oil and the second lubricant was the same oil with a proprietary concentrate of extreme pressure additive of the zinc dialkyldithiophosphate (ZDTP) type.