A high speed video camera was used to record the behaviour of micron-sized particles in a crossflow microfiltration unit. The visualisations were carried out at conditions representative of industrial crossflow microfilters. The dynamics of single particles and of suspensions accumulating at the membrane surface, and the subsequent behaviour of the cake layer formed, were observed. The effect of parameters such as particle size, feed suspension concentration, pH, transmembrane pressure and crossflow velocity on the development of the particle layer and the corresponding permeate flux was investigated. It is shown that, for feed suspensions containing only particulate matter, cake formation is substantially avoided when the shear stress in the crossflow stream is greater than about 10(-6) times the pressure loss across the cake which would otherwise have formed.