Yeast-foulant removal via reverse filtration from cellulose acetate microfiltration membranes was observed in situ using a direct visual observation (DVO) microvideo system. The sizes of the foulant blockages increased with filtration time as cells aggregated on the membrane surface and in the suspension. Coupling of the DVO-determined fractional coverage data with the experimentally determined membrane fluxes indicates that the flow through the cleaned portions of the membranes is nearly straight-through (i.e., little to no radial flow underneath foulant blockages), and the flux through the yeast-covered fraction with backpulsing is over twice the long-term fouled membrane flux without backpulsing. Cell rupture caused by reverse filtration at transmembrane pressures of 3 psi or more led to increased irreversible fouling of the membranes, with scanning electron microscopy pictures revealing a thin blanketing layer of foulant, which is most likely the contents of ruptured cells.