Nowadays there is a wide range of industrial surface treatments that allow important improvements in the behaviour of tools and components, increasing dramatically their lifetime without changing the materials bulk properties. These modifications in the tribological properties are extremely dependent on the chemical composition, as well as on the thickness of the treatment layers. Therefore, depth profiling (carried out by means of different techniques like AES, XPS, SIMS, RBS, etc.) is an important tool only limited by the high cost of time, and by the fact that the maximum analysis depth is restricted to a few micrometres. Glow discharge optical emission spectroscopy solves most of these problems providing a fast and quantitatively reliable way of doing depth profiles of more than 150 mum with a time consumption no longer than 2 h. This work compares the capabilities of rf and dc sources and describes the applicability of GDOES in the analysis of different industrial surface treatments like CVD, PVD and ion implantation. Results present dc and rf GDOES as a powerful method for the characterisation and the quality control of surface treatments. (C) 2004 Elsevier B.V. All rights reserved.