An experimental study of the influence of several contaminant types on the surface indentation in EHL contacts is presented. An original lubrication system with a controlled level of contamination has been developed. The contaminant distribution and concentration are measured on-line by an automatic particle counter called CM20. Experiments are conducted on a two-disk machine with different operating conditions. The oil is a synthetic one qualified under the MIL-L-23699 specification. An optical profilometer is used to describe the indent topography and concentration. The test bench is described and the experimental procedure is presented. Particles from four different materials (SAE Fine Test Dust, M50 steel, SiC, B6C) with several size ranges have been tested. Results show the influence of the particle nature and size on the indentation features i.e. dent shape and concentration.