New technology for on-line particle size analysis of mineral slurries has opened up new applications for particle size measurement. In some cases the particle size distribution of the final concentrate is an important quality issue. This article discusses established on-line particle size analysis technologies and presents experiences on the use of a new technique employing laser diffraction in several minerals processing operations. The main features of the new size analyser are a simple dilution system and multiple scattering correction algorithm, which allows wide solids content variations of diluted sample in the measurement cell. The following applications are discussed: Blaine number measurement of Fe concentrate before pelletizing, grinding of variable batches of ore and paste thickener Control.