The FBRM instrument is a 'powerful' tool developed by Lasentec as an 'in situ' particle monitoring technique for inline real-time measurement of particle size. This technique was successfully used to monitor steady-state operation in a modified MSMPR crystallizer. The FBRM technique was also used to estimate crystallization kinetics. The FBRM particle size measurements were complimented by an in-line process video imaging (PVI) system developed 'in-house, (Microscopy and Microanalysis, 6 (Suppl. 2) (2000) 996-997), to visualize habit and crystal behaviour within an MSMPR crystallizer. A comparison of the steady-state crystal size distributions measured by low angle light scattering (LALLS) and FBRM was made, showing poor sensitivity of the FBRM technique to particles of less than I Pin hence the technique was not suitable for the measurement of crystallization kinetics for this organic system. (C) 2004 Elsevier B.V. All rights reserved.