A technique has been devised to measure the weight of dust on filter bags inside a working filter. The output signals from load cells installed into the top and bottom bag mounts are combined with a ＇lift＇ factor to correct for the effect of the pressure drop across the filter, and are then expressed as a bag weight. Monitoring of this bag weight parameter during several successive filtration cycles has provided filtration research with a clear view of dust cake build-up and release processes. Some initial observations of missed, or ineffective, shakes, as well as the timing of cake dislodgment and the behaviour of the bag tension during the shake cleaning, are reported.