The intermittent initial period of crossflow microfiltration has been studied, and the nature of fouling-layer deposits ascertained by simple physical inspection. At low crossflow velocity, a visible solid deposit was formed on the inside of the tubular membrane, but at high velocities no such layer could be detected. In this regime, fouling was controlled by the concentration polarisation phenomenon. The initial flux in these cases was restored by stopping the apparatus for a few seconds. Cyclical stop-start operation as a way of increasing permeate production is discussed.