Permeate flux decline in dead-end microfiltration of whey protein isolate solutions is studied, using disc-type ceramic membranes of nominal pore size 0.8 mu m. The tests involve five successive filtration cycles, under fixed filtration pressure, with intermediate backwashing. Flux decline analysis and membrane resistance are employed to determine fouling mechanisms, with respect to applied pressure, in the range 2.5-10psi. Permeate and retentate concentration data complement the permeation rate measurements. Both irreversible and reversible fouling is identified for the backwashing mode employed. Data interpretation suggests that more rapid fouling, as well as significant surface-layer "compaction" effects may occur at the higher pressures employed. There is evidence that irreversible fouling effectively develops during the first cycle of the tests (of 30 min duration) and apparently does not significantly increase later on; however, reversible fouling occurs through the entire filtration series, being more intense during the first minutes of each cycle. The effect of protein aggregates is investigated with the aid of DLS measurements and filtration tests with prefiltered solutions; it appears that whey protein aggregates present in the solution, are responsible (almost entirely) for the observed membrane fouling. An effective membrane cleaning procedure is proposed. Finally, the possible advantage of operating large-pore size MF (for the process considered) at rather low pressure is suggested. (c) 2006 Elsevier B.V. All rights reserved.