Special features of on-stream XRF analysis systems are described. Controlled sampling with onstream analysers is explored; metallurgical multistage sampling using MSA samplers capable of sampling the streams of up to 60– 18000 m³/h. A new flow cell is designed making possible to ensure the availability of a fresh representative sample in the critical area for analysis and an analyser automatic window changer that considerably increases X-ray tube lifetime. Wave-dispersed and energy- dispersed X-ray fluorescent spectrometers (WD/ED-XRF) as well as process control issues are briefly discussed.