The fouling effect of different antifoams and compounds of antifoams on crossflow filtration membranes is studied by on-line measurement of the permeation flow during the concentration of suspensions of baker’s yeasts in reverse osmosis water (initial yeast concentration, 9 g/L dry matter; concentration factor, 6). The experiments are carried out on three types of tubular mineral microfiltration membranes, two types of flat-sheet organic microfiltration membranes, and one ultrafiltration mineral membrane. The compounds tested are principally silicone oils, silica + silicone based antifoams, and a modified organic antifoam (modified polyalcoxyester). The presence of 100 ppm of any of these compounds in the initial feed suspension does not cause a measurable effect for all membranes compared to the fouling due to yeasts. The fouling of a microfiltration mineral membrane due to the amount of silicone antifoam equivalent to 2 years of industrial operation (that is, cumulated in one run without yeast, 25,000 ppm in 12 L feed solution) does not increase beyond the fouling resulting from filtration of the reference yeast suspension.