Outokumpu Company has gone a long way in the last 20 years in the development and application of WDXRF-techniques in on-stream analysis of slurries in ore concentrators. The applications in which the samples were in solution form came only about 4 years ago when these analyzers were used for the first time in hydrometallurgical plants, During the past 15 years many improvements have been made in most parts of the equipment to Biake the performance and reliability better. The most important work to improve the analytical capability of the analyzer has been done on the spectrometers and detectors. This has resulted in better sensitivities and has given the possibility to go down to ppm levels in many determinations. The technical details of the improvements have been presented in several papers (1-4).