The use of laser light scattering technology, as applied by the Focused Beam Reflectance Measurement (FBRM) probe from Lasentec, for the in-line monitoring of particle size was investigated. In particular, the effects of probe position and orientation were studied for a dilute agitated aqueous particulate suspension of known particle size distribution in a number of vessels. In all cases, the normalised chord length distribution recorded with the FBRM system was consistent with the theoretically predicted distribution. However, the total number of counts measured was a function both of solids concentration and probe location. Optimum probe location is dependent on the ease with which the solid phase can be suspended with the available agitation system and on the associated dominant flow direction within the vessel.